Surpriiiiiise! There’s no sign if Sprint’s just testing things or if they’ve just been caught in the act before they got a chance to send out a press release, but reports are coming in that Sprint’s 4G network has just gone live in San Francisco.

Our eagle-eyed buddy Marin of IntoMobile noticed the network’s new-found SF presence this morning, when his Sprint Overdrive suddenly lived up to its name. Download speeds jumped from the standard megabit-or-so per second up to anywhere from 3 to 9 megabits per second.

Now, before you get too excited: this doesn’t appear to cover all of San Francisco right now — skyscrapers and hills make coverage difficult, you know? However, Marin says he’s seeing the 4G juices flow in live around Embarcadero, SoMa, and the Financial District.

Got a 4G device, like the EVO, Epic 4G, or Overdrive and live in San Francisco? Give it a quick reboot, and let us know how things go.