Daniel Eran Dilger:

CDMA (voice) and EVDO (3G data), unlike GSM/HSDPA, can’t perform simultaneous voice and data at once. It also lacks GSM’s inherent ability to conference multiple parties at once into the same call. ”EVDO rev A“ has the technical capacity to handle a voice and data connection at once, but this requires handling the voice conversation via VoIP as data rather than a normal cellular voice circuit, something the Palm Pre can’t do (and apparently no other Sprint or Verizon phones can do either).

This is the same reason both Mr. Dilger and I feel that Apple will stay with AT&T for  at least awhile longer.