1:43pm: A source tells ESPN.com's Marc Stein (Twitter link) that Terry is expected to give the Mavericks a chance to match the three-year offer before agreeing to sign with Boston.
1:38pm: A. Sherrod Blakely of CSNNE.com confirms (via Twitter) that the Celtics are close to signing Terry for their full mid-level exception. Spears adds (via Twitter) that the deal is expected to be for three years.
1:18pm: The Celtics are in "final discussions" on terms of a multiyear contract with Jason Terry, according to Marc J. Spears of Yahoo! Sports (via Twitter). Considering the Celtics have an agreement with Kevin Garnett, are close to re-signing Jeff Green, and are still talking to Ray Allen and Brandon Bass, it's unlikely they have any free cap space, so they're probably looking to use their mid-level exception on Terry.
If Boston reaches an agreement with Terry, it doesn't necessarily mean the club won't bring back Allen. Coach Doc Rivers recently told Spears that he could envision the Celtics signing both Terry and Allen for next year's squad. According to Alex Kennedy of HoopsWorld (via Twitter), the C's were interested in O.J. Mayo, but because Mayo was seeking more than the mid-level exception, they moved on to Plan B, which was Terry.
The Suns, Mavericks, Grizzlies, and Clippers were also said to have Terry on their radars.