BBDB has a dial interface which allows you to call an external interface to make a call. This is done by modifying bbdb-dial-function. This is an example which interfaces with Skype to make a call on Mac OS X.
(setq bbdb-dial-function
'(lambda (phone-number)
(do-applescript
(concat
"tell application \"Skype\"\n"
"send command \"CALL +" phone-number "\" script name \"Call from BBDB\"\n"
"end tell"))))