We've used a contract with cingular and T-mobile Speak Easy prepaid plan, and people I work with have tried a variety of services when we are in the US.

I got my Speak Easy SIM from a wholesaler for I think 30 usd, expired over a year from start up, minutes did not expire for about 8 months after activation. Initial minutes that is. But any refill minutes expire if unused after 90 days. And the number died after a year or so I believe due to non use. I had no problems in LA or SanDiego or LasVegas on T-Mobile (mostly SanDiego). Minutes were easy to refill (to find refill cards). I personally had no problem with it but used it when I was travelling in and out of the US not stationed there for a long time at any one stay.

T-Mobile has Get More Plus plan that is 59.99 per month, 1000 minutes, unlimted weekend minutes, unlimited weeknight minutes. The Get More plan is 39.99 per month, 1000 minutes, but does not include unlimted weekend or weeknight minutes. They require a one year contact only.

If you talk enough for the 1000 minutes a month then a preapid plan or pay as you go would be much more expensive and you should get the year plan.

An associate has Cingular 450 plan, and Cingular now has Nation 850 w/ rollover for 59.99 per month, 850 minutes, unlimited night and weekends. Nation 600 is 49.99 per month, 600 minutes, unlimted weekend / night. Both rollover minutes. But that is out of San Diego, I'm not sure what plans are available out of LA specificially. And I think he had a two year contract but signed up on line not at a store specifically. Then there's family plan's prepaid plans and others for Cingular as well.

Overall, IMHO cell plans for travellers going to the USA are terrible compared to other countries and that always amazed me.