There is no reason to focus on T-Mobile or Sprint as much as they should on VZW, the largest. It's gonna get good.
Not to mention there's still whispers of a T-Mobile/Sprint merger, which would put the combined company neck and neck with both VZW and AT&T, all at around 90million subscribers, give or take a few million.
Frankly what Verizon really need to do right now is hurry up and start getting their LTE network deployed. They have pledged to have it available in up to 30 cities by the end of the year though. - Leaked Documents and LTE SIM Show Verizon 4G Launch Is Imminent
They are definitely losing a significant amount of people in certain areas to Sprint, due to Sprint's 4G network having been live for a while already and the fact that they're about to launch their second 4G Android device. I believe the Evo has already become the biggest selling device in their history and 4G obviously plays a big part in that.