How old is your iPhone? We talking pre-6s, or a Sprint/Verizon CDMA model? If so, there could be considerable reception issues even beyond just poor T-Mo regional coverage given they've pretty much shut down nearly all of their 2G/3G voice network for band 12 4G VoLTE service. The other thing to remember is that MVNOs like Mint only use network-native towers, so T-Mobile postpaid will have far better coverage because of roaming agreements that you won't have access to otherwise.
CellMapper.net also shows hit and miss coverage for band 12 in that part of Boulder.
All this said, I won't be surprised if you possibly still see at least one other person on these forums try and sell you on Mint anyway because of "WiFi calling" fallback or whatnot, and they'll be sure to include their trashy little $25+ referral code link while talking about how great the service is while hand-waiving away their actual problems and terms of service. Always ask yourself if somebody is recommending something to you because it's actually the best choice for you, or if they're recommending it to you because of what they get out of it.
The easier option with coverage questions is to just recommend using either an AT&T or Verizon MVNO when just going at it blindly, and the choice between AT&T and Verizon depends on whether your iPhone is the GSM (go AT&T) or CDMA (go Verizon) model.
As for which MVNO?
RedPocket offers monthly plans starting at $10/month for 1000 minutes, unlimited texts and 1GB of data on all four networks, and all their monthly priced "unlimited" talk and text plans with xGB of unthrottled data are still cheaper than Mint's prices in their three and six month blocks, and though Mint appears cheaper than RedPocket for introductory and annual plan pricing, RedPocket still offers their same plans at a discounted annual price just as cheap as Mint
through their Ebay store. Given everyone wants a one-size recommendation and they don't like to research these days, I just suggest RedPocket now as their prices are competitive, their support reasonably competent, they offer plans on all the major networks, MMS works for iPhone even on the AT&T network with them, and they don't try to flummox people through the grotesquely meaningless
overuse and
abuse of the word "unlimited". Just be sure to read the terms of service with any provider you choose, including them. At least RedPocket gives you the ability to opt-out of CPNI data collection, which is more than I can say for some other MVNOs.
My wife and I have used them ourselves for the past couple years on the AT&T network without any issue, and although they technically offer a referral program, you will see no such link from me. I won't even sign up for it. Take it all for what it's worth.
Best of luck, and enjoy your time in Colorado.
