My company is looking at hosted VOIP providers for our work phones. I've noticed that some of the providers we are looking at say they can work with any SIP client, while others have proprietary clients only they work with. I recall reading various discussions about people using SIP on the N8x0 but never really knew what that was about and didn't have the need, so I kind of skipped by it.

Now looking more closely it seems to be just as confusing as I remember. I've come across a lot of posts talking about setting things up, but the end goal generally seems to be about personal use for free or cheap calls, while I'm more interested in integrating into a business setup.

So does anyone care to explain what i would need to get my N900 to work this way? I've seen mention of a SIP client built directly into the phone, but also seen people mentioning using 3rd party apps like Fring (which I've also noticed mentioned on a couple of hosted VOIP provider websites), any reason to go one way or the other? Assuming I can get everything setup, does this allow me to make calls on my N800 using "data" rather than voice minutes?

Any other useful things to know about using the N900 as a SIP client?