Speaking with us this morning at Mobile World Congress, T-Mobile USA's Andrew Sherrard confirmed that the carrier would proceed straight to its just-announced LTE network after wrapping deployment of 42Mbps HSPA+, already a high watermark for HSPA+ in the US that'll be supported on upcoming devices like the HTC One S and Samsung Galaxy S Blaze 4G.
T-Mobile had previously said (as recently as CES in January) that it would be moving to 84Mbps — a move that would require additional antennas and the refarming of some 2G spectrum in the 1900MHz PCS band, which has already been reported to be underway in some markets. It seems that the "challenger strategy" LTE announcement complete supersedes those 84Mbps plans, or T-Mobile had been publicly using the 84Mbps language as a placeholder for LTE while it evaluated the viability of rolling out an LTE network in the constrained spectrum that it has available.
To be successful, both 84Mbps and LTE require the same surgical refarming of PCS upfront, which will reduce the network's total 2G capacity as its subscribers transition to 3G-capable devices. Sherrard notes that T-Mobile won't be selling any more handsets that don't support 3G, which means that the total 2G load on the network will reduce over time; in other words, no one should feel an impact from losing that 2G capacity.
Logically, the decision to skip 84Mbps makes sense — the HSPA+ technology roadmap may still have plenty of runway, but LTE has even more. And considering that T-Mobile needs to invest capital into the refarming operation either way, it may as well get LTE under its belt.