...I think other than wifi and voice call this cant happen with most phones. The only way you could do it without two radios in the phone (you think you have battery problems now?) would be to have software in the phone that would calculate bandwidth available and setup the split of voice and data or just some general simultaneous voice and data split setting. I think they havent gone there because call quality and network coverage is already a source of problems and addin this would put more strain on those things.
I havent researched it. im pretty sure there is alot out there on this.
Yup after googling
http://wireless.agilent.com/rfcomms/refdocs/gsmgprs/gen_bse_dtm.php
looks like nokia's can do both and its called dual transfer mode DTM
it requires a special component in the phone and software on the carrier's switches - so its Hardware on both ends and Software
the only way you're gonna do it on sprint is via voip and data at the same time or CS (circuit switched - voice call) and wifi
after more looking
EVDO doesnt do simultaneous voice and data
the euro pre version will use UTMS and will be dual mode
http://www.pcmag.com/article2/0,2817,2341178,00.asp
wait for verizon's pre