Mobile television service provider MobiTV announced today that it had passed the 5-million-subscribers mark. This caught our eye, because back in August the service had 4 million subscribers, and at the time we wondered if growth was slowing.

According to MobiTV, the opposite is true. Whereas it took the company 10 months to get from 3 million to 4 million subscribers, it took half that time to add an another million. What gives?

MobiTV co-founder and president Paul Scanlan told me in a phone interview today that the number counts people who actually pay for the service — but it isn’t just people going to MobiTV.com and signing up; it inlcudes direct subscribers as well as those who receive the service as part of a bundled package from Alltel or Sprint. Scanlan declined to provide a breakdown of standalone vs. bundled subscribers.

Scanlan attributed the burst in growth to a number of factors including more sophisticated phones; a wave of interest in doing more with those phones, spawned by the iPhone; carriers that are more willing to bundle the service; and bet