How are the towers going to be handled post merger? T-Mobile's GSM based service vs. Sprint's CDMA service means someone is going to have to win if they're serious about consolidating spectrum and towers.
T-Mobile’s network will form the core of the new network because it’s significantly better, most Sprint devices will support GSM and UMTS 2G/3G standards (while the opposite isn’t true), T-Mobile’s network supports voice over LTE, T-Mobile’s network has significantly more cell sites, etc. Some Sprint sites will be added to the network and Sprint’s spectrum will be as well. Other sites will be divested to Dish.
The CDMA vs GSM divide just isn’t that important today given that carriers should be mostly LTE already.