@Trifele? Your German exchange student, strongly dependent upon their mobile phone model, may have a really bad time trying to use their European smartphone in the United States.
Without knowing the EXACT make and model of the handset in question (and do make sure it's carrier unlocked), it's difficult to provide any meaningful or specific recommendations. I'm not going to talk to you like a five year old, but an adult, and I will try to keep it simple. But there's still a lot of reading to get you up to speed, and I'll try to divide things up for you. Now, let me explain why...
First, a few things to understand as to what's going on currently with the US mobile phone market and access to voice calling:VoLTE is Voice phone service over LTE data networks. This works very differently than the older 3G voice services that nearly any international handset can handle. The rest of the world is happy to leave those legacy 2G/3G networks operational. Oceania (Americas/Australia/Japan - Pacific Rim) and the USA especially, is in a race to shut down and obsolete legacy networks as quickly as possible. This is probably due to equal parts hubris, planned obsolescence, consumerism, and proprietary infighting. No matter what you attribute it to, the consumer is the loser. Even with $1000 big band and network support handsets that can be taken "anywhere" with model consolidation, the world still mostly falls and splits into two models with these handsets, Oceania and Eurasia+Africa, and even "international" handsets may run into trouble here in the USA specifically depending on make and manufacturer and chosen network carrier even if the phone has VoLTE Band 12 support.
T-Mobile is currently shutting off all their legacy 2G/3G networks and pushing phone service to VoLTE only.
AT&T will be shutting off their legacy 3G networks and pushing phone service to VoLTE only at the beginning of next year.
Verizon will be shutting off their legacy CDMA networks and pushing phone service to VoLTE only throughout the next year.
VoLTE deployment and handset interoperability in the United States between carriers is an absolute charlie foxtrot, as you'll quickly learn. VoLTE
Band 12 is supposed to be the common voice band for the USA and for roaming agreements between carriers (
edit: memory error and misprint, I think Band 12 [700MHz C block] was originally intended, but we've gotten Bands 2 and 4 as the common carrier bands for VoLTE roaming which is the same PCS/AWS spectrum that T-Mo notoriously used for GSM 2G/3G voice services for years that had terrible building penetration and forced them to be the first US adopter of Voice over WiFi a decade ago until they shut it off last year), but roaming access to
Band 12 any of these bands isn't the same as native network access...
AT&T primarily uses a basic, internationally compatible VoLTE implementation on multiple LTE bands (mostly 2 and 12). However, they've set up basic
VoLTE access to whitelisted IMEI (phone serial number) handsets only, which means AT&T only branded handsets. They're notorious for not supporting fully compatible international handsets from working on their network thus far, despite being able to work, because their IMEI
isn't on the list. There are ways around this, but it requires a postpaid AT&T account, and being technical enough to know what model handset (that's actually reasonably close to what you actually have) to lie to the AT&T rep to get the IMEI manually accepted and added to their whitelist. So, even if you stuck in an AT&T SIM card today and the phone works today (which it likely would given their 3G network still being operational), it will likely stop working in under five months.
T-Mobile primarily uses LTE Band 12 (a commonly supported international LTE data band supported on international handsets), however,
their VoLTE implementation is proprietary and requires VoLTE software "certification". As an example, aftermarket Android ROMs like LineageOS that even support and easily do VoLTE calling in the rest of the world rarely ever work on T-Mobile, even if VoLTE worked on the handset with T-Mobile before flashing a new OS onto the phone. Because of this, many "international" Android handsets actually might not work on T-Mobile in the United States. This said, with the student from Germany, it's possible they're already on T-Mobile there and bought their handset from T-Mobile Germany. This increases odds of compatibility specifically for them.
Verizon uses bog standard VoLTE implementations for their voice services, so no hinky stuff like IMEI whitelists or proprietary "certification" and implementation.
Unfortunately, LTE Band 13 is used for most of their voice services and for SIM activation.
This isn't to say there aren't patches in their network that don't offer Band 12 coverage (they're mostly urban) (
edit: lol, error in my brain and LTE band cheat sheet, Verizon has no Band 12 spectrum, I was thinking of USCC the other remaining CDMA network - sorry, I'm getting old and the memory isn't what it used to be)
but to activate a SIM card for service and to get regular network coverage for making calls, you need a handset that specifically has LTE Band 13. There are only four countries (and barely more carriers than the country count) that even use LTE Band 13: USA, Canada, Bolivia, and Belize. So, there's that.
Awkward growing pains and all that. I'm hoping they'll all stop with these shenanigans after they all fully transition over to VoLTE and shut off the legacy networks and just let phones be taken from network to network again once carrier unlocked like back in the GSM 2G/3G days, but where's the fun and profit in
not forcing people to buy new handsets when switching carriers by preventing network interoperability through minor technical loopholes.
"Why does this matter? Don't kids these days just use data and video chat and internet based communications apps like Zoom and WhatsApp?" I can hear someone say. You bring it up yourself. Two Words:
Emergency Services. 911 phone support isn't the worst idea (especially with a callback number available to dispatchers), and the VoLTE implementation here appears to be really cocking up that whole guaranteed access to 911, even without a SIM card, that mobile handsets are supposed to have... though I'm digressing a bit.
Bottom line, if the phone won't work here in the USA with one of the big three, the phone won't work, and you'll probably have to pick up a new handset for them. So, be prepared for that possibility.
Unrelated and secondary to the big elephant of network compatibility, another consideration might be
international calling and texting support by the phone plan itself so the kid has a way of keeping in touch with friends and family back home by means other than internet based apps only, for both safety and convenience reasons related to potential emergency situations. I know it's being skirted "to save money", but the savings aren't that much to have versus not have. Even with congested data traffic, actual VoLTE calls and SMS messages are going to be prioritized over common data access during a larger crisis. Not all MVNOs have international text and calling support, and some have more than others depending on the country in question. So, something else to keep in mind while shopping as well.
So,
TL;DR: T-Mobile based MVNOs with good international calling and texting plans might be your best option if your exchange student's handset is from T-Mobile back home or is known to already work on T-Mobile here in the States, but it's still a crapshoot without researching for compatibility first. Also, buying a full year prepaid plan could be a good way to save some cash if you're willing to take the risk. But it's critical to know if the phone is going to work at all in the first place. T-Mo based MVNOs can potentially be the cheapest of the big three these days, too. This said, if you don't have great T-Mo coverage, go with the network that has the best coverage in your area. And if you need a new phone and you already have a phone for another network for cheap/free that has VoLTE support, go with the network that phone supports.
With this in mind, I will make an MVNO recommendation.
Red Pocket offers plans on all three networks, sells a $10 SIM card kit with SIM cards provided for all three networks and their month to month "unlimited" calling prices are still some of the cheapest you'll find on all three networks. They also offer international direct dial and unlimited minutes to Germany (land lines) and limited minutes (29-105 depending on network) to cellphones with their unlimited calling plans. This path guarantees a single recommendation provider that will have a SIM card that'll work on whatever network/device has to be used, and provides international calling to boot. You'll be looking at around $240 plus tax and fees for the year at the baseline for an "unlimited" plan billed monthly ($180 for the year through the eBay store), but there are cheaper options.
If a really small plan is on the table, Red Pocket has a
500 minute 500 SMS and 500MB plan on all three networks for $10/month, or their $99 annual plan sold through their
Ebay store that provides 1000 minutes, unlimited texts and 1GB of data. I believe the international calling is limited with these plans, however.
Last thought as it's been mentioned by others: Be aware of
Mint's actual prices, and note that they charge extra per minute on calls to Germany. Those alluring per month prices that you're advertised on the intro three months are only the annual plan pricing for calls to the US/Canada/Mexico. Otherwise, their prices are just about equal to or more expensive per month to Red Pocket. It doesn't make financial sense to use them in this situation unless you're 100% certain a T-Mo MVNO will work, and you're willing to agree to their terms and services and be potentially willing to lose the balance of any money paid if they decide to terminate the account early for vague and dubious usage "abuse" like too much data of a certain type or too many calls... which, honestly,
read the legal contracts with any provider you use as any provider promising "unlimited" anything will have various gotchas. The risk just gets dicier with pre-paying service months in advance.
Minimum price through Mint will be $180 plus tax and fees and per minute fees to Germany if you buy a full year up front, otherwise, the cheapest you'll get on their cheapest plan without paying for three or more unneeded months will be $240 plus tax and fees, or buying 15 months will be $225 plus tax and fees.
Edited because I forgot about the $180 annual plan from RedPocket.
Edited again because my memory and notes are a little fuzzy at this point, and a couple details were wrong... nothing that changes the reality of VoLTE interoperability in this country, but wrong none the less. Sorry about that.