Software
Software-based VoIP applications, especially in the form of softphones installed on the computer, might face some software compatibility with Windows 7. This will not entirely depend on Microsoft as such, unless there is some deliberate attempt from Microsoft to block some service, of which there is no sign so far, but rather on how these third party VoIP application developers readjust their products to Windows 7. So far, some complaints have been heard here and there about this program not working and that program being silent. There will surely be a moment before everyone gets adapted to the new Windows, until the latter becomes as 'stable' (take the word with a pinch of salt and with a glass of relativity) as Windows XP has been, or until it confirms as a flop as Vista has been.
Skype is among those applications that are working on Windows 7. I hope this makes the half a billion Skype users sigh. Versions 3.8, 4 and 4.1 of Skype work with Windows 7, although some minor problems have been reported here and there.
There are dozens of other VoIP applications around and each one will be carrying a different story, at worst. So the best thing is to try and see, or check on their sites for updates and releases. There are some applications that have been tested positive so far. They include Google Talk, Windows Live Messenger (if this doesn't work, then what will?), and many-in-one applications like Trillian and Digsby.
It is interesting to note that Yahoo! Messenger 9.0 voice-calling feature is not compatible, according to what we have gathered so far.
Web-Based VoIP Services
When you use web-based VoIP services like Jajah and TringMe, since you have nothing to install on your computer, the compatibility issue with Windows 7 is no problem. Windows 7 even has improvements in plug-in support for browsers. For instance, ActiveX plug-ins can now be installed without administrative privileges and the new feature called 'Windows Web Services' will welcome more and more third party VoIP services through browsers and other Internet software.
Hardware
Hardware devices and compatibility are better dealt with in Windows 7. With previous versions of Windows, you could only have one registered audio device. With Windows 7, you can have two, one as default sound device and another one as default communication device. This means you can have your own communication-specific hardware on your computer, making it a permanent communication center.
On the other hand, mobility between machines might be a problem in Windows 7 with USB headsets, handhelds and other voice communication devices. Unlike with XP and Vista, Windows 7 has disabled the automatic driver installation for USB devices, for security reasons. Those who communicate on public machines and through USB communication devices and keep changing computer might find this inconvenient.
