I don't think that's likely to happen that Apple will go to LTE directly. Eventually over time, yes.
LTE is still new and the infrastructure is only in specific, and strategic places and has not been rolled out to all major and moderate metro areas yet. So, just as Apple first first introduced the iPhone 2G model, where everyone was wondering why Apple chose to come out only with 2G as the initial introduction instead of 3G, Apple won't move to pre-4G (LTE) yet until there is sufficient critical mass in the LTE infrastructure (easier adoption by more people) and this LTE infrastructure won't happen until mid-2011 or end of 2011, or later.
Carriers don't invest heavily in CDMA technology and then rip them out to replace them with LTE. They usually move to new technologies gradually e.g. LTE, consolidate, or overlay, and/or move the older technologies e.g. CDMA to smaller or rural areas.
I think what's more likely to happen is that for 2010+, Apple will introduce the Apple OS4 and CDMA iPhone (to grab existing CDMA market share from other phone manufacturers), and in 2011/2012, they'll come out with their next iPhone 5 (aka iPhone pre-4G or LTE). That way their future version of iPhone will be usable on the more readily available LTE infrastructure.
Most people always think that people can install such cell technologies as fast as people can design them. But in actual truth, the overall time taken to manage the roll out and implement LTE (or any new technology) is very long.
GSM is still around and was introduced back in 1991. That's nearly 19+ years ago. CDMA will be around and maybe for just as long but definitely longer than when LTE will be implemented for the masses.
Anyways, that's my 2 cents. It definitely will be interesting to see which way Apple moves to. I'm for the CDMA iPhone rumour due to the additional milking revenue that Apple will get with introducing the CDMA iPhone in 2010 and another LTE iPhone in 2011/12.
I forgot to mention, that if Apple moves to an LTE iPhone, and there is no LTE signal supported in a specific regional area, then there is no fallback technology unlike the HSPA/2G/GSM that is possible with the existing iPhones. That's why Apple won't be moving to LTE yet since the infrastructure is not there until 2011.
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