1) WhatsApp pretty much runs on
anything. Personally, I'm not a fan due to security and privacy concerns, but if you're entrenched you're entrenched.
2) Blackberry requires BIS to work without
massive hacks, workarounds, and replacement apps. BIS also costs extra money with carriers (more of a problem with prepaid than postpaid, though). If you want a Blackberry-like experience without BIS costs, look into getting a carrier unlocked Nokia Symbian S60 device. Something like the e63, e71, e73 (older models) or if you prefer a bit more modern, the e5 or e6 running S60 Anna/Belle. They're all at least quad-band GSM handsets and easily found relatively affordable carrier unlocked, the most expensive being the
e6 (current generation) running about $250.
3) GSM is going to be the way to go for you for multiple reasons: a) because you still travel overseas and need a phone that supports global GSM, b) you need a broad chunk of coverage in the US due to being on the road, c) being a Blackberry fan, Nokia's the closest you'll get to the BB experience without BIS, and Nokia doesn't make Symbian handsets for CDMA carriers.
4) Postpaid is probably the way to go. Not because of the volume of calls (which is light), not because of SMS volume (again, very light), only partially because of the data usage (which should and could be cut down a bit more, but still forgivable if you're looking at living on the road for the most part), but mostly because of the apparently heavy travel combined with the international communications requirement. You'll need to be able to roam off-network with data access, which means postpaid GSM account.
Unfortunately, it's gonna cost you if you're really looking to keep it simple. You're looking at a baseline of around $60/month plus taxes on postpaid... so figure closer to $72 after everyone takes their pound of flesh. That said, T-Mobile is likely your best option. I feel absolutely filthy for having to recommend this, but you'd need to select the $50/month "unlimited" package with 500MB of data plus the $10 international package (for 200 fargin' minutes a month and 50 text messages - *shudder* what a waste) to get yourself covered. The problem isn't even so much the international, it's the mobility with data and as guaranteed as possible coverage that's slaughtering your bottom line.
Now, if you find you can survive purely on the T-Mobile network without finding yourself roaming off network at all, you might be better suited to giving
P'tel/
Giv Mobile a look (same company, one brand does charitable donations off your billing). $40/month gets you set up with some international communications perks and gives you 250MB of data at full 3G speeds and 2G throttling after that point (you may be stuck at 2G EDGE speeds anyway most places if you only have a quad-band GSM handset as T-Mo needs pentaband models like the e73 to access their higher speed network in some markets - 2G EDGE is plenty though for e-mail and WhatsApp).
Overall, if you had to pick access to only one GSM network, however, AT&T would have more complete national coverage. If you potentially want to try and go the AT&T only approach, given the international necessity,
RedPocket would be your go-to. With your data needs, however, expect to drop $50/month.
If you could absolutely gut your data usage down to nearly nothing (well south of 100MB/month), and could get away with T-Mobile only coverage, P'tel's Real PayGo would be the clear winner as you could probably get away with less than $20/month. Airvoice is strictly off the table, because international calling/texting costs are insane.
Bottom line? International + data + roaming = expensive. The only way to reduce costs is to eliminate one or more of those factors. I think that's about as detailed an analysis as you're gonna get.
If you want to thank me, visit the
website, buy the Nokia e6 through the link above,
donate some money to tornado relief efforts in Oklahoma, or do a little of everything, or, just ignore the blatant tin cup rattling. :)