A T-Mobile RF engineer, claiming to be “heavily involved” in the carrier’s LTE upgrades and network modernization plans, started an AMA on Reddit this morning. Not surprisingly, many of the questions were iPhone and Apple-related. The questions ranged from how much 2G/EDGE traffic the carrier’s network sees from iPhone customers as it begins to transition that spectrum to WCDMA to where T-Mobile plans to upgrade its network coverage next:

Q: Can you talk briefly about how much traffic on GERAN you see from iPhone customers? How much of a catch-22 is that situation for moving that PCS spectrum dedicated to it over to WCDMA?

A: We have about a million iphones on our network now. 99.9% of their traffic is 2G/EDGE only right now, so obviously their load is dwarfed by everything else. The iphone is a significant part of the modernization project. Once implemented, iphones will work on U1900 at much higher speeds.

Spectrum is always a limitation. With the software that exists now, you will not be able to do dual carrier split between AWS and PCS. That’s supposed to be fixed in the future, but I don’t know a timeline on it.

Q: Are the upgrades targeting 2G areas first or current 3G/4G areas first? I’ve always figured it would be more sensible to upgrade the 2G-only areas first to get the network fully upgraded.

A: Upgrades are focusing on the core metro areas, very similar to the areas that recieved 3G/4G first…I would love to expand the 4G coverage area, but that’s not happening at the moment.

A confirmation that T-Mobile will roll out 5MHz FDD-LTE when the network is launched, opposed to Verizon’s and AT&T’s 10 MHz FDD, also appeared in the engineer’s responses:

We’re going with remote radios as much as we can, for LTE, UMTS, and GSM….LTE will launch with a single 10 MHz channel, 5 up, 5 down.

We will update you here if any other interesting questions/answers pop up on the engineer’s AMA.