First off, let me give full credit to who is providing this information: if you're not following Erik Erlendsson on Twitter, you're robbing yourself of great Lightning coverage.
That being said, Erik had some nuggets from this afternoon's press conference with GM Steve Yzerman that he shared on the subject of defense and the 2014 NHL free agency period which officially commences on July 1:
#tblightning GM Steve Yzerman said he has utilized the open window to speak to UFA and reached out to some Dmen, didn't mention names, tho— Erik Erlendsson (@erlendssonTBO) June 25, 2014
Yzerman said ideally he'd like to acquire a young D under contract via trade, but admits that's difficult to pull off— Erik Erlendsson (@erlendssonTBO) June 25, 2014
You may commence your speculation now as to who Yzerman has talked to.
As for the trade talk -- it comes down to cost to acquire (and how well that player fits both on the roster and under the cap). While Tampa Bay has assets to play around with in the 2014 NHL draft, Yzerman likely puts higher value on the draft picks worth than potential trade partners.