You can get inexpensive pre-paid sim card for local domestic calls but here are the caveats:
1. TMO 3G network not compatible for iPhone; only option is AT&T network
2. There are a couple of threads on "US sim cards for data" - my sense is there are quite limited and not cheap
http://www.flyertalk.com/forum/searc...archid=6594537
3. Incoming calls stateside are not free (unfortunately)
4. International calls out on pre-paid are going to be fairly expensive
You might be better off
1. using your home country account to access emails; google maps might be costly with your home network (?).
2. use wifi hotspot with skype for international calls
3. get second mobile phone with pre-paid sim card for local calls. they are cheap. Best Buy, Walmart, Radio Shack, AT&T n TMO websites are just a few places that sell them.