New comScore data shows that Facebook and Twitter use has skyrocketed on mobile devices over the past year, and that on-the-go MySpace use is now on the decline, according to MediaPost.

Here are the numbers: Facebook now sees 25.1 million mobile users as of January 2010, which is more than double the January 2009 total. Twitter grew to 4.7 million during the same period, which is four times the year-ago total, the report said.

MySpace, meanwhile, fell 7 percent to 11.4 million for January 2010. Note that all of these numbers are for mobile Web and SMS use, not dedicated mobile app use, which covers another 6 million users.

Finally, the report said that over 30 percent of smartphone users visit social networking sites from their devices. That’s up from 22.5 percent last year, whereas only 7 percent of regular cell phone users do the same thing.