Personally I think VOIP is headed into the nursing home, not coming out of the nursery. Still, it's one of those names that people will probably always associate with internet telephony, much like MP3 will be synonymous with digital audio files for years to come. That does't help your names though.
voice-over-internet-protocol.com: is just too long. $0
wi-fi-voip.com: The hyphens kill it and the non-hyphenated one is taken. $0