One of the cool things about Voice Over Internet Protocol (VOIP) is the use of a softphone. A softphone is essentially just what it sounds like -- a software-driven phone. In a business environment, if your company had a VOIP system, you could be away from your desk and use a laptop or PDA anywhere there was an Internet connection to access all of your phone features using softphone software. There would be no perceptible difference to people that were calling you or to people you were calling, and all of the same features you had at your desk phone -- caller ID, voicemail, etc. -- would work on the softphone software interface.
While this sounds great for corporations that are able to afford dedicated private switches, how does a consumer get these benefits? Well, I've talked before about Vonage, a home VOIP provider (connect their box to your home high-speed connection, pay the monthly service, and make normal phone calls). Well, Vonage now offers softphone support to it subscribers. Imagine being able to go on vacation, jack into the high-speed port in your hotel room, run the softphone software on your laptop, and make calls and check voicemail without being charged the exorbitant hotel rates (anyone see the massive business model change for hotels?). Even better, imagine using your PDA at your local Starbuck's, singing onto the wireless Internet and being able to receive and make calls as if you were sitting in your home office.
Fast forward to about the middle of the summer an imagine most smartphones having WiFi access built into them, so you could run the softphone program in parallel to your regular cell service whenever you had wireless Internet connectivity; all other times, you could use your softphone software to forward your work/home number to your cell number (I would imagine that once these phones start hitting the market, someone will program some software that allows you to very easily accomplish these tasks on your smartphone).