VoIP does provide a low-cost way to call people in the U.S., either computer-to-computer, computer-to-telephone or telephone-to-telephone (through a VoIP modem and high-speed cable or DSL connection). There are also some really great "free" VoIP services, such as Skype, that let you make computer-to-computer or computer-to-telephone calls, at reduced international rates.
However, you don't need a wireless network to use a VoIP system. You can access VoIP through your Wi-Fi connected computer and a home or office wireless router. So wireless does offer an added degree of flexibility.
I have been using VoIP for about six months now and have discovered that it is not entirely perfect. There is a price to pay in quality of service and reliability for a cheaper phone bill. But it does come through most times and has a definite return on investment (ROI).
As for wireless: All you need to enable wireless in your office is a wireless access point and a Wi-Fi card or wireless-enabled PC. All Wi-Fi operates on the same standard unlicensed 802.11 spectrum, which means you can pick up an AP at your local computer or electronic store, plug it into an Ethernet port and you are soon on the air.
Before you do this in your office, though, make sure your IT department knows about it and sanctions the installation of the AP. If you put an AP in your cubicle without authorization and "light up" everything around you for about 200-300 ft, then you are probably violating IT policy and will soon be looking for another job. You will also be opening up a wireless window into your company's network for anybody and everybody with a Wi-Fi enabled system. Not a good thing.
Once you install an authorized AP and leave your office, that gateway doesn't go anywhere. If you connect through the local Wi-Fi hotspot then you are using their AP to get on the Internet to access your email. This is an important distinction. Because there may be little or no security on this connection, you really have to be careful what you are sending or receiving. Most mobile workers access a separate virtual private network (VPN) from outside Wi-Fi locations, which provides a dependable layer of security.
As I said earlier, though, all Wi-Fi is based on standard communications architectures, so you can use your wireless notebook anywhere there is a Wi-Fi signal. However, you may not be able to use outside systems, since they are protected or encrypted. You may also have to pay a fee for using a Wi-Fi hotspot.