Skype for iPhone could debut at the trade show that begins April 1 in Las Vegas next week, Malik speculates. Industry watchers have anticipated an iPhone version for some time, particularly since the popular service already runs on other mobile devices. In addition to Skype for Windows Mobile and Skype Lite for Java phones, there's a version for phones like the T-Mobile G1.

While Skype's mobile ambitions are good for iPhone users, the VoIP service won't bring the end of standard voice-call service anytime soon. As PC World's Liane Cassavoy of four mobile VoIP apps -- EQO, Skuku, Skype for Windows Mobile, and Truphone -- mobile VoIP call quality isn't quite there yet, and the cost savings aren't that great.

"Most notably, the call quality remains iffy at best, and in some instances it's absolutely abominable. Also, depending on your calling habits, you may not see any savings at all. Most services still charge a per-minute rate, so you'll save on domestic calls only if you've exceeded your regular voice plan's allotment (in which case you might still be better off upgrading your voice plan)."

Cassavoy does point out, however, that international callers can save big bucks by using a mobile VoIP service.

While Skype for iPhone may not offer immediate benefits for everyone, the service has plenty of potential in the near future. If the , which may appear as early sometime this summer, includes video capture, Skype could turn the iPhone into a portable video conferencing device. That may not happen immediately, of course, but AT&T's upcoming 4G Long-Term Evolution (LTE) broadband network, slated to , could very well have bandwidth necessary to make two-way, real-time video a popular app, particularly among business users.