In the wake of the announcement of the Apple iPhone 4 on Verizon, one question I’ve seen come up is if the Verizon version will be able to use voice and data simultaneously, as on AT&T’s version. Â Typically, some of the answers to the question range from the half-right to the hilariously incorrect with a lot of confusion in between. I think a better question would be: Does it even matter at this point?
In order to understand why AT&T touts simultaneous voice and data as an advantage, you have to look at their network. I’ll get to the iPhone in a bit.
UMTS (and by extension HSPA/HSPA+) uses a 5MHz channel to transmit voice and data over the air, with the capability to further “split” the channel into two 2.5MHz sub-channels in case one person is sending both voice and data at the same time.Â In contrast, Verizon’s CDMA network uses a much smaller 1.25MHz channel to send voice and data, with no way to split the channel further, forcing either data access and no voice calls or voice calls and no data access.
With that out of the way, you might be wondering how Verizon is able to offer Skype Mobile on its phones since it requires both a voice and data plan. Simple: a little network and software trick called IMS or Internet Multimedia Subsystem. Â IMS is built into a CDMA EVDO Rev. A network and overlay by converting the initial outgoing call into a data session, “moving it” onto the data network via application and network flags. The carrier has to turn on the IMS on the backend in order for simultaneous voice/data to work and the developer has to include the support for IMS into the program, otherwise it’s not going to work.
Now, back to the iPhone. Reports started coming out last summer that Verizon was working on Voice Over Revision A for the iPhone. This is IMS, it is not new nor is it exclusive to the iPhone as many erroneously reported.
Now that its been confirmed that that the iPhone 4 will not support simultaneous data/voice, is browsing and talking on the phone really that important to current and potential iPhone users? Only if you care about bullet points. The reality is that few, if any people will actually use such a feature frequently enough to take it into account as a purchasing decision and only see it as a novelty.
Sure, it would be nice to talk on a headset and browse on Mobile Safari on Verizon’s network at the same time, but that would lead to intense battery drain and temperature issues as the chipset would be handling a phone call over VOIP and a data session over EVDO, something that’s conveniently overlooked on AT&T’s claims.Â In fact, the only people that see it as an advantage are those that care more about spec sheets than real-world utility. Just try using AT&T’s impacted data network… with half the bandwidth you normally get.
Should you worry about the possible availability or lack of simultaneous voice/data on the Verizon iPhone? In my opinion, not one bit.