What can I get out of Verizon because of T-Mobile?

I travel a lot for business and I've used T-Mobile before so I know what I'd get if I switched back. I do know that if I threaten to go to T-Mobile because of the new offer to cover my early termination fee they are likely to offer something but I've never really pulled this kind of a move before. What could I ask for and what could I expect? I think in reality what I'd really like is the offer of a lower bill but not a temporary credit for the remainder of my contract but an actually lower rate.

I'm looking for suggestions and tips from anyone out there with some experience. Thanks!