I think Nokia’s approach to SIP in the N-Series phones is quite useful and sensible. GizmoVoIP–ie. calling phone numbers via Gizmo Project’s open SIP gateway–is one example of how to configure Nokia’s SIP stack to get extra voice functionality from your N-Series phone. But I’ve also toyed around with using the Nokia N95 with Asterisk, and I’m looking forward to trying the phone out with one of my clients’ in-house VoIP systems.

The cool thing about the N95′s support of SIP is that it’s trouble-free and easy to set up. You establish whether you want VoIP calls or Cell calls to be placed, by default, and the phone will attempt using your preferred transport. If VoIP is unavailable, then the call goes out cell. If it’s available, then it goes out VoIP. Same deal if Cell is the preference and VoIP is the secondary option. This lets you use SIP as the backup plan.

But it’s so much cooler than just this. Since the phone can receive incoming SIP calls as well, you can register with any SIP gateway where you have credentials. This means being able to receive calls from your office VoIP PBX, whether you’re in the office or out at a WiFi hotspot somewhere (notwithstanding firewalls, etc.).  So, why bother with pricey convergence features like Avaya’s EC500 when you can just register your cell phone directly with the PBX? Sure, there are instances where you still need stuff like EC500–for example, if you’re outside the reach of WiFi coverage.

Anyway, the point is–having solid SIP (not error-prone like UTStarComm and Linksys) on the cellular handset is a huge step towards worry-free convergence, and I’d like to see Nokia start pushing SIP and WiFI down through its product line to its lower-end phones. The day is coming, I’m sure. Nokia is probably the only cell phone vendor that doesn’t “need” the big wireless carriers to maintain its consumer appeal. They’re kind of the Apple of the phone business, albeit much more dominant than Apple is in their space.

And it’s a mighty big shame open SIP won’t be appearing on the iPhone.