OS/2 Wireless Users Mailing List <os2-wireless_users@2rosenthals.com>
AT&T will unlock their phones but they make it a little more difficult these days than in the past. T-Mobile will unlock their phones without much trouble if you meet certain qualifications.
You can get very cheap unlock codes for most AT&T phones on eBay from seller "swiftsales714". (I've bought several from them.)
The best forum for information on this seems to be howardforums.com.