I don't really buy into this Papelbon declining theory, but I do agree with ital that trading for him and then having his salary on the team would take away from a much larger concern, being the rotation. Shoring up the bullpen isn't a terrible idea either, but at 15 something million a year, yeah I don't know.
Uehara so far has done pretty well in the 9th, I know he's only had a couple outings, but he's looked good. The team still has Tazawa to fall back on as well.. and I'm sure there will be plenty of MUCH cheaper options available at the deadline that could be almost if not AS effective as Papelbon has been or possibly could be.
Now if the sox are going to dump a bunch of prospects onto the Phillies, it had better be for Cliff Lee, not Jonathan Papelbon.