MGCP Support V6812-MGCP Vodavi

I am trying to find out if these phones can be registered without the need of costly media gateway. OR can I build a media gateway using asterisk 1.4/1.6 I have about 16 Vodavi V6812-MGCP phones that I need to use all in new working order. (Also accepting offers for the phones). I would prefer to use them in my office but have no real knowledge of MGCP protocols.

Can these phones be flashed to use SIP protocols rather than MGCP? Please advise you can PM or post directly here. Thank you.