- Toy Providers - These are providers that use proprietary protocols and you're stuck using their software. These providers have little to distinguish them from regular Instant Messaging - as IM as long had Voice capabilities.
- Consumer-Unfriendly providers. These are providers that use open protocols but don't let their users benefit from it.
- Consumer-Friendly providers. Open protocols, with the basic information needed to use their service from whatever client the user wants, not just the provider's own client.
I'd say that it's really a spectrum from 1 to 2 to 3. Tiscali and Skype are certainly in the toy provider realm, I call them toy providers because what they are offering is little more than a toy - something to play with, but not much else. AOL's service is based on SIP (which means it had the potential to be more than a toy) but modified so that the SIP base only benefits "partners" of AOL, not AOL's users - a consumer unfriendly act that leaves AIM Phoneline as little more than a toy. Some providers may have terms in their T&C's that state that you can only use their software with the service even though they use open protocols - this is consumer unfriendly behaviour that is absurd - it's like having a website and requiring everyone to use the website's own browser. Others may use open protocols but not federate with other providers (but at least allow users to use whatever software they want). And then there are the providers that are open and federated and provide the needed information to use whatever software their users want (such as Gizmo).