>Moving away from CDMA and supporting VoLTE is bound to happen even if Sprint stays solo. Other operators have plans to sunset CDMA (e.g. end 2019 for Verizon), and at some point it doesn't make sense to stay with a now legacy standard with no traction.
They backed themselves into a corner because they use unusual spectrum and don't have the funds to upgrade all their towers to modern technologies. It makes sense when you can't afford to upgrade.
T-Mobile has no plans to sunset GSM yet because it costs them very little to maintain, uses little spectrum, and allows legacy equipment to stay on the network. Some even predict they'll sunset WCDMA before GSM.
Sprint spent 5 years on the network vision project, it rolled LTE out to their entire footprint, and was an all but forklift upgrade to their field infrastructure. The only components left from the original site usually was the power cabinet, and the tower structure itself, everything else was new.
CDMA costs no more for sprint to keep on the air then GSM does for T-Mobile.
They backed themselves into a corner because they use unusual spectrum and don't have the funds to upgrade all their towers to modern technologies. It makes sense when you can't afford to upgrade.
T-Mobile has no plans to sunset GSM yet because it costs them very little to maintain, uses little spectrum, and allows legacy equipment to stay on the network. Some even predict they'll sunset WCDMA before GSM.