From my limited experience with cell phones, most companies will NOT let you use it as a modem, without a data plan at least as expensive as a separate modem. I think (as impossible as that sounds) that T Mobile allows this for relatively cheap. All the cell phones have the capability to be used in so many ways, that are locked down by the providers. This way they can make more $$ of you to let you do things. A short list is: Photo exchange via bluetooth to ANY other phone, computer, or access point. (But this is why (for example) Verizon makes you pay the extra charge for PIXFLIX, and downloading charges.) Tethered modem. Most companies want to charge you extra for the privilege to use what the phone can already do by design!` An interesting part of this is, if you are paying for unlimited data on a cell phone to surf the net, they can’t tell HOW you are surfing, whether over the phone, or via a laptop! So if you can unlock your phone to use it as a tethered modem (or untethered), they can’t tell! The phone is viable to be used as an untethered modem too, But most companies (that allow it) force you to buy the $100 modem cable or pay big bucks for a wireless plan. I believe this is called revenue enhancement by the companies, But I call it thievery. Since you work overseas, you have probably seen how much cell phones can do when they are unrestricted. You can pay for parking at a parking meter, via bluetooth, you can pay for postage, and more stuff I have forgotten about. So I don’t feel bad when someone unlocks a phone to release it’s full capability. You can compare different providers. They often have the same phone (but with different model numbers) At one provider the phone only provides cell service, but for more, you can buy extra features. At another provider you can do everything the phone is capable of. Apple comes to mind here. The difference is, one company has more (or less) of the features locked out than others.
Now for the illegal stuff… Not that I have ever done this
Howardforums.com has a multitude of phone info to let you (if you are quite adventurous) to go into the phones programming and unlock the restrictions on how the phones are limited by the various providers. But be warned, you can permanently damage the phone, and unless you are creative, and have phone insurance, you will have to pay full price for a replacement.
One difference you will find, Smart Phones chew through the batteries like hell when you are using all the functions. You will be required to always have a charging cable with you.