From the Globe:
Former NBA shooting guard Reggie Miller admitted earlier today on the Dan Patrick Show that he received calls from both the Celtics and Cavaliers earlier this season asking if he would be interested in playing. It was the second inquiry in the last two years that the Celtics have made into the availability of Miller's services.
Judging by the looks of this photo, Reggie is enjoying retirement too much to come back and play for the C's.