After years of speculation, it looks like VoIP is finally about to hit the wireless market. Let's take a look at the intersection of VoIP and mobile phones and see what it means for you.

While popular peer-to-peer VoIP service Skype claims that mobile VoIP is still too expensive, startup Fring has launched a new mobile client that works seamlessly with Skype.

Fring is a free download (just like Skype) that gives users access to both Skype and rival peer-to-peer VoIP service Google Talk over both 3G and Wi-Fi networks on their Symbian-based smartphones.

That's pretty cool, but Fring is a little upstart. So what?

Well, another startup, Jajah, this week announced a new VoIP service that lets smartphone users make free international calls. Unlike Fring, Jajah's newest offering, called Jajah Mobile Web, requires no special software downloads. Users just enter Jajah's mobile site in their handset's browser, type in their Jajah user name and password, and they can make a one-click call to any entry in their Jajah address book, all free of charge.

OK, so you're still skeptical. Well, the third piece of mobile VoIP news this week is from Microsoft (and they're hardly an upstart).

News broke yesterday of Microsoft's latest mobile OS, Windows Mobile 6. One of the new features of Windows Mobile 6 will give the OS access to VoIP. The new technology will enable carriers and device makers to add VoIP functionality to Windows Mobile devices. Partners will supposedly announce VoIP functions for the platform in the next year.

What does all this mean for you? If you connect the dots, I think you can begin to see that mobile VoIP is finally coming into the mainstream. There are already several Symbian-based mobile VoIP clients and it looks like Windows Mobile is about to make it standard for that platform. It's probably a good bet that mobile VoIP will also show up on other platforms, including BlackBerry and Palm, in the next few months.

I also think it's likely that some of Microsoft's partners will release dual-mode VoIP Windows Mobile 6 devices targeted at the enterprise. These smartphones and PDAs will be designed to help companies trim their cell phone costs and better integrate mobility into their corporate telephony systems.

But, we'll have to wait until next week in Barcelona to see what else is coming.