VOIP with WIFI cellphone - what is SIP for?

Session Initiation Protocol. According to Wikipedia:

The Session Initiation Protocol (SIP) is a signaling protocol, widely used for controlling multimedia communication sessions such as voice and video calls over Internet Protocol (IP). Other feasible application examples include video conferencing, streaming multimedia distribution, instant messaging, presence information and online games. The protocol can be used for creating, modifying and terminating two-party (unicast) or multiparty (multicast) sessions consisting of one or several media streams. The modification can involve changing addresses or ports, inviting more participants, adding or deleting media streams, etc.

In practice, its a standard for VoIP. Its open (not sure of its exact open source/proprietary status) and is used by lots of providers, rather than Skype which uses its own closed protocol.

You can sign up to a VoIP provider and make cheap calls, same as skype.

Advantages: if you use a local provider, you can get a local number (there is a charge for this). In NZ I use 2talk; there is also VFX by Xnet. 028 numbers are free (at least from 2talk), or $7 a month for a local (e.g. Wellington 04, Auckland 09) number.

Generally, I also find the call quality much better than skype, and much much better than skype via fring which goes via fring's servers.

Last I checked (its been a while) the NZ providers were also by and large cheaper than skype. Most have free on net calling.

Disadvantages: can't call skype contacts.

A further advangtage (though this is for your Nokia, rather than SIP per se): you can use Nokia's excellent native SIP application to set up default VoIP calls. i.e. you're in a hotspot, your phone will automatically make a call via VoIP. Outside a hotspot, automatic cell call. No need to access different applications etc. All from your standard address book.

2talk has instructions here.

EDIT: spelling

freemark

mdf