Despite my admitted Mac-fanboy status, I do use other technologies. Notably, we use Skype for work and have had great success with it.
A recent poll, however, suggests that Google Voice is more popular than Skype. For lawyers, what works better?
Why Google Voice is better
It is cheaper, with the relatively low cost of zero. Kinda. If you use Google Voice through your cell phone, it will use your phone’s minutes. If you call using your computer, it will not use your minutes (well, it should not). There are ways to make sure all calls are free though.
Google Voice can also used from inside of Gmail, which is great, if you use Gmail for work. It will also transcribe your voicemail messages (with limited proficiency) and you can also setup specific caller ID preferences, when your phone should ring, etc. Google Voice is constantly changing for the better and with Google behind it, you can almost guarantee it will continue to work well.
Why Skype is better
Skype is not free, but at $2.99 a month (and a discount if you purchase a year), it is really cheap. It can be used over Wi-Fi or 3G and it will not up eat your cell phone minutes.
Skype also allows video conferencing, which is nice for business, and for talking to co-workers. Skype does not provide voicemail transcription, which is something of a bummer. Skype is available all over the world, so if you make lots of international calls, it might be preferable to Gmail.
The bottom line is that both are great services that do not cost much at all and either service is much cheaper than paying for a landline. I prefer Skype, mostly because it has always worked well, and I firmly believe if it is not broken, there is no need to fix it.