Here's a switch. Porn giant Vivid Entertainment claims it's been violated ... by a phone. Ouch.

Vivid has fired off a cease and desist letter to HTC America, claiming the mobile phone maker's newest model -- Vivid -- infringes on its trademark.

Lawyers for Vivid ... the company that gave us the Kim Kardashian sex tape ... claim consumers might get confused and think Vivid is behind the phone ... not in a sexual way, of course.

The letter threatens that if HTC doesn't change the name of the phone by Monday, they're headed to court.

Come to think of it ... a Vivid Entertainment phone would be awesome. Think of the screensaver.