s710a is the north american counterpart of s700. Just like Nokia 6620 for 6600, SE T616 for T610. Cingular offers 850Mhz coverage as well as 1900 MHz in USA. T-Mobile, follows european standards and strictly offers 1900MHz only.
If you have service with Cingular and intend to try out this phone, I would suggest you to wait till s710a is released. If you are with TMO you can try out s700. Also TMO as of today - hasnt rolled out edge.