[Sprint Samsung Galaxy S III] bitbang3r:
I'm not 100% sure, but I think I remember the guy from s4gru mentioning once that LTE is like 1xRTT & CDMA voice (and unlike EVDO) in the sense that towers work as a team to receive & decode LTE, so a phone halfway between two towers with overlapping footprints typically experiences a *much* stronger & robust connection than a phone that's nearly adjacent to (but visible to ONLY) one tower.

The net result is that a "sparse" partly-deployed LTE network (or a single tower serving an entire isolated island, like Key West) will never work as well as it does in an inner suburb of a big city where users are surrounded by 2 or 3 visible towers at all times. Factor in the "cliff effect" (at a certain point, the usability of LTE at a given signal strength "falls off a cliff"), and disconnects & thrashing are unsurprising.

In areas with sparse LTE & backhaul-starved unimproved cell sites, the irony is that the ideal operating mode would be "LTE whenever possible, falling back to 1xRTT when it's not." Unfortunately, that would require radio-level programming that's not possible for end users to do (the FCC requires "robust" bootloader security & encryption for radio firmware, though some might argue that phone mfrs. *could* legally allow licensed ham radio operators to mod their own radio firmware if they wanted to).

As a practical matter, Sprint can't do it (even if they agree in principle) because a single tower site can't handle very many simultaneous 1xRTT users at any given point in time. 1xRTT (as deployed, not in theory) has real scalability limits, and those limits were all blown off the scale the day Sprint started selling iPhones. It would also adversely impact a tower's circuit-switched voice capacity, because 1xRTT uses the same spectrum (and T1) as voice calls (most pre-NV towers have two T1 lines... one shared by voice, 1xRTT, and control data, and one shared by all EVDO users). The net result is that if we (xda users) all started aggressively using 1xRTT in preference to EVDO on towers that are backhaul-starved *anyway*, other users would start having calls go straight to voicemail without ringing whenever their nearest tower was "maxed out" for 1x/voice capacity.

Anyway, just to wrap the essay up, 1xrtt has two concrete advantages over EVDO when it comes to augmenting LTE:

* faster setup/teardown. Basically "instant", as long as the tower site has capacity to take you when you try to join.

* for some reason I don't fully understand, it's impossible for our phones to simultaneously have active LTE and EVDO sessions (one "up", but quiet & inactive), but IS physically possible to do it with LTE/Wimax & 1xRTT (in fact, our phones DO it every time they poll for incoming voice calls & SMS when there's also an active LTE or Wimax connection).

Sprint doesn't bother to distinguish between 1xRTT & Evdo, and just has phones fully break one session before trying to bring up the other (this is what causes most of our "thrashing grief"). However, tower-capacity permitting, different firmware *could* follow a strategy optimized for minimizing latency & maximizing robustness and availability by maintaining simultaneous live LTE/Wimax and 1xRTT data sessions, and switching between them at will from byte to byte. Or even establishing a VPN over the pair of wireless links, transmitting everything over both, then using the copy that arrives first & aborting or discarding the datagram that arrives second. (About 8 years ago, I worked on a similar project involving IDSL (ISDN where all 3 channels are bonded for data only... roughly 160kbps symmetric over 20+ miles of copper) & satellite broadband. It worked great, except Hughes kept FAP'ing us at absurdly low thresholds because their 'abuse' algorithm brutally punished 'opaque' traffic).