Why CDMA phones do not transmit or receive data while voice call?

To answer your question, CDMA phones cannot transmit or receive data during voice calls. The AT&T campaign was a direct attack on Iphones running on Verizon services. The Verizon based Iphones runs on a CDMA connection and hence can't receive data and take voice calls at the same time. So basically, what happens is that of you get a call while data transfer is taking place, it gets interrupted and likewise, if you are on a call but you want to check out a website at the same time, you have to hang up on the call.

Now this is a technical problem, as CDMA connections cannot operate both the services simultaneously. This is because in the CDMA series standards, which is used by Verizon there are two different channels of 1.25MHz which are assigned to both the different services. Voice calls run on 1xRTT while a completely different service, which is EvDO (Evolution: data only)  is for data transfer. So at a time, only one service can run.

There are two solutions for this, the first being use of WCDMA, which is used in AT&T 3g phones where you can access both services simultaneously as voice calls and data transfer run on the same 5Mhz channel. The other solution is if Verizon and Iphone develop an Iphone which is based on LTE services, which can operate bot voice calls and data transfers at the same time.