I have been doing a little looking around and this seems like the best option.... if anyone has any better ideas or agrees, please post, i'd be interested to know those that have done this.

Am thinking of spending some time in the USA later on this year.  Currently I have a quad band GSM, 850/2100 HSDPA phone. 

Was thinking of using an AT&T prepaid SIM to keep in touch with people while i'm over there.  I'm not too worried about data, but more being about to make phonecalls and txt if I need to.  Would rather use a local SIM than get ripped off by Vodafone's roaming charges.

I'm aware coverage isn't as good as in NZ, but I'm not too worried about that.  I'll be spending most of my time in cities as well.

AT&T seem to have the best fit of network for NZ phones as far as I can see.  T-Mobile look OK, but I notice their 3G is 1700/2100.

:edit: sorry if this is the wrong sub-forum, couldn't find a better match.