T-Mobile USA has confirmed that it will need a spectrum partner by 2014 or 2015 in order to build sufficient LTE capability, though the carrier refuses to reveal which companies it might look to work with. Meanwhile, the carrier believes 10-percent of those leaving its network are shifting to AT&T for the iPhone; in response, it plans to offer sub-$100 Android smartphones with $10 data plans.
"Deutsche Telekom is exploring various options to acquire additional spectrum and reduce the gap regarding economies of scale compared with its larger competitors, including partnering with other companies" T-Mobile statement
The exact timeline for T-Mobile's LTE roll-out has not been made public. The carrier has said it will stick with HSPA+ until LTE "devices are readily available and once device quality is on par" with the HSPA+ handsets coming to market presently, "although that will probably not be for a few years." 42Mbps HSPA+ is expected to debut later this year.
Verizon launched an LTE network in late 2010, and AT&T plans to do the same in 2011; both could be potential partners for T-Mobile, though AT&T's GSM background might make legacy compatibility more straightforward than Verizon's existing CDMA network. T-Mobile expects the LTE roll-out to cost between $1bn and $2bn.