Has anything changed with Verizon's ability to have voice and data on the 4S? Or is their network still limited?
Well, VZW did introduce changes to their network known as SVDO which allows simultaneous voice and data... the HTC Thunderbolt takes advantage of this.
No, nothing changed. You won't be able to call and surf at the same time.
I don't know if the COMM chip in the new iPhone supports this yet. If it did, Apple would have made a special slide taunting this, and so would Verizon in their page by now.