VoIP over 802.11 wireless

Today's wireless VoIP phones use H.323 or proprietary protocols to connect to VoIP call servers. 802.11 is merely the first hop in the IP route from phone to call server. Some type of (proprietary) quality of service mechanism is often applied to the wireless hop. Examples of Wi-Fi enabled VoIP phones include SpectraLink NetLink and Symbol NetVision.

Retail, healthcare, manufacturing, and other companies install private VoIP systems like this. Wireless phones within a given system can communicate with each other. Outgoing calls can be forward to the public-switched telephone network (PSTN), but a PBX gateway is usually required to receive calls from the PSTN. The PBX relays calls to the server, which routes them to VoIP phones. Public VoIP providers like Vonage extend this capability to the general population. IP packets traverse the public Internet to reach the provider's call server, where calls are bridged to/from the PSTN.

Increasingly, PDAs are being equipped with VoIP telephony features -- for example, TeleSym's SymPhone client runs on Pocket PCs. A company that installs their own SymPhone call server can support calls between Wi-Fi-enabled Pocket PCs. A SymPhone PBX connector to the public switched telephone network is needed to also place and receive outside calls.

To answer your question, let's consider how TeleSym's solution works in a public Internet access hot spot: http://www.searchNetworking.com/infoCenter/originalContent/0,,sid7_gci877644,00.html