I go without contract.

Airfire: $35/month plus sales tax = unlimited data, talk, text.
This is great for local service, but I often travel and the phone will not work.

So...
Straighttalk: $45/month plus sales tax = unlimited 3G data, talk, text.
This is a nationwide plan. Its actually on the ATT network if you buy a Nokia E71. And the best part, the SIM card can be put into an iPhone and the iPhone will work fine with just a couple quick settings. Not sure about visual voicemail though, that may not work. But its the cheapest way to get an iPhone on ATT and be unlimited!

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1991 560 SEL / 185k miles
1992 750il / 17k miles - project car