I've done the Skype install on my 770 2007HE, and have had some success.
I can place a call to another skype user on a Linux computer without an error message. However, when I attempt to call another user who is using a skype phone device (unknown brand) I get the "no common codec" message.
Is it possible or likely that skype compares software on each end of the call when starting, and that some are incompatible? Possibly some codec is missing on the 770?