Most VoIP services use SIP as the underlying technology for their service. SIP is an international standard, which means it is widely used and also relatively interoperable — a SIP phone is a SIP phone, no matter who makes it and whether it's wired, wireless, or embedded in your skull.
Because SIP is so standardized and widely used, manufacturers of Wi-Fi gear are making and selling SIP Wi-Fi phones that you can use with most major VoIP providers. Skype does not use SIP (at least not in an interoperable way — Skype's VoIP protocols are their "secret sauce" and they're not telling!). So these phones won't work with your Skype account.
Consider the following when choosing a Wi-Fi VoIP phone:
- Wi-Fi standards supported: You'll want a phone that supports at least 802.11g. No 802.11n Wi-Fi VoIP phones are currently on the market, but expect to see these trickle onto the market and replace the 802.11g models.
- Battery life: Battery life is a crucial issue with any cordless (or cellular) phone. Unfortunately, Wi-Fi was not designed to be a low-power technology suitable for use with small phone batteries. (It uses much more power than, for example, a mobile phone radio system.) So battery life is the Achilles' heel of many Wi-Fi VoIP phones. Check the different manufacturers' rated battery life, see how easy it is to recharge (many phones come with a cradle you can drop them in, just as you do with a home cordless phone), and see how easy it is to replace the battery should it wear out.
- Security support: Most of these Wi-Fi phones will not work in a WPA2 Enterprise/802.1X network. Most do support WPA and WPA2 Personal, the minimum level of security you should shoot for.
- Web browser support: If you plan on using the Wi-Fi phone in a lot of hot spot environments, consider a model that includes a built-in web browser to provide a mechanism for logging into hot spots that require use of a captive portal log-in page.
- Codec support: The codec is the voice compression algorithm used by a VoIP system. A number of different codecs are used by VoIP service providers. A Wi-Fi VoIP phone must support the codecs (such as G.711) used by your service provider. (The best way to determine these codecs is to look in the support section of your VoIP provider's Web site or to call tech support.)
- Everything else: A lot of little things may or may not be important to you as you examine Wi-Fi VoIP phones. Examples here could include the size and quality of the screen, support for additional applications on the phone (such as e-mail or IM), button and keypad quality, and the user interface and menus.
The most important criterion of a Wi-Fi VoIP phone is whether or not it will work with your VoIP service. SIP VoIP services are based on standards, and any SIP-compliant phone should work with any SIP-compliant VoIP service (which is most services). Many VoIP service providers, however — in an attempt to keep their support overhead to a minimum — don't explicitly support phones and devices on their network beyond the phones they sell or provide to their customers. Some providers may even make it hard for you to find the information about their service's servers and IP addresses needed to configure your phone.
There are a number of manufacturers of Wi-Fi VoIP phones, ranging from big networking companies down to small specialist companies you've never heard of. Some of the more popular include