If you're using Wifi data, yes. Or possibly using internationally with a GSM sim card, and using a GSM provider... but using Verizon 3G-CDMA data, no - that's not possible.
I might be wrong but I think thats a nah on Verizon and yes you can on AT&T. It is a carrier feature not a phone feature. Maybe someone else can chime and let you know if Verizon has changed something or if these Iphone4S GSM/CDMA make that possible
Not currently on Verizon only some of their 4g phones allow you to talk and surf at the same time and thunderbolt is only one you can over both 3g and 4g