Looking for a pre-paid SIM card (for a GSM phone) for USA (ideally
also Canada) that provides data access also (GPRS).

Ideally something that doesn't expire after 20 or 30 days.

(I'm currently using a TMobile card - it's fine, but they have no GPRS
card available(??)  - As long as I use it on a regular basis it
remains "alive" and I don't need to buy a new card/change the number.

I visit the States and Canada about 5 times a year, so would prefer a
card that is OK with no calls for the 2 months when I'm away.)

Thanks