To excessively or with great apparent pleasure send cell phone text messages. Normally with fervent pecking at the keyboard with dueling thumbs in an almost rhythmic movement. The texter may also be quite unaware of their surroundings, focusing all efforts on proper spelling of cryptic jumbles of letters and acronyms.
He completely lost track of time while thumbsterbating with his girlfriend all night at the party. He would thumbsterbate with his girlfriend at every given opportunity.