For those looking to chop their monthly ATT or TMO bills, Straight Talk just introduced a BringYourOwnPhone program for $45/month unlimited everything (and $60/month with an unlimited Int'l calling add-on).

Phones can be unlocked or locked to either ATT or TMO (order the SIM card that matches where your phone is currently used), and phones require a simple APN edit to get data working (although many locked iPhone models will have a problem with MMS). The network your phone has access to is at least as good as the native coverage with either ATT or TMO (or both depending on your phone and frequencies)

Ordering is here: http://www.straighttalksim.com/

One caveat - no int'l roaming, so if your phone is locked to either ATT or TMO, it will be a brick when abroad without wifi.