B737 Captain reported receiving notification from a Flight Attendant that a catering truck had struck the aircraft service door. The aircraft was moved forward to dislodge the catering truck and a new aircraft was assigned for the flight.

Narrative

During the boarding process the aft FAs called up to have me come look at something. I proceeded to the back and saw the catering truck stuck to the aft door 2L. We called Local Maintenance and they quickly arrived. There plan of action was to pull the plane forward a foot or so to dislodge it. Boarding was completed; crew was briefed and checklists done - minus one door. Ground crew communication was established and the move was performed. Maintenance called up and told us that the damage was worse than expected. We coordinated with Operations; deplaned and were quickly assigned a new jet.