Boston has not signed Turner because they have too many people on the roster and are trying to move some of them first.
I've heard this before, but it doesn't make a whole lot of sense, since there are no roster limits during the summer, and the C's have guys they can easily cut in camp to get down to 15. If they want Turner, they can sign him.
I think the real issue comes with questions of sign and trades, and deciding which exception to use to sign him.
I remember seeing some thing about the MLE, and how if they move some players they wouldn't have to use the full on Turner. Not sure if thats true, but it would makes sense why they are holding off.
The issue is that when you officially sign a player, you have use a salary exception. For the Celtics to sign Turner today, they have two choices:
1) Sign him with the taxpayer MLE (assuming he's agreed to a contract for this amount or less). Using this exception prevents the C's from using the BAE or saving more of the larger non-taxpayer MLE later in the offseason.
2) Release 1-2 non-guaranteed contracts and sign him with the non-taxpayer MLE. This gives them the ability to sign another player with the remaining portion of the exemption, and for up to four years. This is the exception used to sign JOhnson and Babb last year. It let's you take a flyer on a D-league player midseason and keep him very cost-controlled if it works out. Of course, doing this requires someone, probably Bogans, to be released, and Danny would like to keep trying to use that contract in a trade for a little while longer.
At some point, either option 1 or 2 will happen if a trade to clear space doesn't occur first. My guess is on choice 2.