Different Approaches for Voice over LTE ?

There may be different approaches by different mobile operators (read Verizon and ATT) for voice over LTE solution. Primarily this has to do with their LTE deployment strategy. AT&T will go with a phased approach wherein they will deploy LTE in certain markets and cover the rest with HSPA+. This seems to be their strategy which makes sense since HSPA+ also can match ractical UL/DL speeds that LTE provide.

Tmo just announced their HSPA+ rollout in few cities which AT&T should like. So AT&T might adopt a Circuit switched over HSPA approach for 2-3 years before they decide to overlay LTE with nationwide footprint.

Verizon on the other hand is overlaying its current CDMA network with an LTE. So seem likely to adopt IMS core for their LTE implementing VCC.

I read an interesting article about a possible third approach for LTE voice .. and that Dual Radio with single SIM . Verizon surely seems to be using this with Thunderbolt, which is bound to save them some CAPEX (in near term) for not implementing IMS core. But going forward they will certainly upgrade to IMS core to incorporate burgeoning APP world.

For Sprint only time will tell how will they rollout LTE. But they certainly can take a leaf out of this Malaysian operator :)