VoIP phones are cellular enter the consumer market. In the United States, only T-Mobile HotSpot @ Home service allows customers to make cellular calls through a VoIP network. HotSpot @ Home relies on a device called a dual-mode phone cell.

Dual-mode cell phones contain both a regular cellular radio and Wi-Fi (802.11 b / g) radio. The Wi-Fi radio enables the cell phone to connect to a wireless network to the Internet via a wireless router. If you have a wireless router to the Internet in your home, or if you're sitting in a Starbucks with access to wireless Internet, you can use your cell phone to make VoIP calls. Here's how it works:
When the cell phone is within range of a wireless Internet network, the phone automatically recognizes and connects to the network.
Any calls you initiate on the wireless network go through the Internet as VoIP calls. With HotSpot @ Home, all VoIP calls are free.
If the phone is out of range of a wireless signal to the Internet, it automatically switches to the regular cellular network and calls are charged as usual.
Dual-mode phones can seamlessly hand of Wi-Fi to cellular (and vice versa) in the middle of a call as you enter and exit the Wi-Fi networks

Similar to dual-mode cellular phones are phones Wi-Fi Wi-Fi phones are not technically cell phones because they have only one radio Wi-Fi, no cellular radio. The Wi-Fi phones look like cell phones (small, light and combined), but can only make calls when you are connected to a wireless Internet network. This means that all calls Wi-Fi networks are VoIP calls.

The Wi-Fi phones are useful in large companies and offices with their own extensive wireless networks. And could prove to be the next big thing, with the expanding market for municipal Wi-Fi. [Source: Dr. Dobb's Portal]. Imagine that your whole town was covered by a network high speed wireless. This means cheap (or free) VoIP calls wherever you go.

In England, a company called Hutchinson 3G (or simply 3) has partnered with the popular VoIP service Skype to introduce the 3 Skypephone. The Skypephone allows users to make free calls from cellular phone to other Skype users. The cell phone can also make regular telephone calls to non-Skype users for reasonable expenses. Here's how it works:
To make a Skype call using the 3 Skypephone, you must be on 3 of the cellular network.
To make a Skype call, find a Skype user in the address book from your phone and press the big "Skype" button.
The call will first of 3 GSM cellular network to a fixed line internet, which then connects the call to Skype [source: mobileSift].
From your 3 Skypephone, you can make free VoIP calls to other Skype users whether they have a Skypephone or not. You can talk to Skype users on their PC or other products using Skype VoIP.