No, there is a limit on leased tuners, and only one "Dish'n it Up" per 12 month period.
I got a ViP722 to replace my ViP622 when it started to have the HDMI connector problem. A few months later, Dish informed me that they had a greater need for my 721 than I did. So I said fine, I was going to up to another ViP DVR in a few months anyway, let's do a deal. They said no, only one "Dish'n" deal per year. I said "Well, the only reason I did the last one is because YOUR ViP622 went bad, and the only reason I want to do another one now is you want MY owned 721 back, which is working fine." CSR scurried off to super, came back "OK."
Then we negotiated price. Scurry, scurry, "OK." So now I have two ViP722s and a 508.
I had considered a ViP612, but read too much about it, but moreso, it really didn't have the specs of the ViP722. So it was worth it to me to pay a bit more, even though both HDTVs with the ViP722 DVRs remain in Single mode and have never been, and likely will never be, connected to a second TV. I knew not to go with another ViP622- besides, I might want to dl an HD movie on either box one day.
Of course, since I was upgrading to a second HD DVR, I "had" to get a second HDTV. Wife bought it, that's all that matters.
Oh yeah- you had a question.
Dish will make you an offer to turn in your 625 and get a ViP722. If you're not due for a promotion, you might have to dicker. They will, of course, want coin of the realm, and a 2 yr commitment. I'd guess you'll pay $75 up front, after exhibiting some reluctance, maybe $50.
I've never before been under a commitment with Dish. Doesn't matter, I'm happy with Dish and going nowhere. I've got external HDDs on both boxes, and WAY more stuff recorded than I'm ever likely to be able to watch in my lifetime.