I've just found an iPhone SIP client that more-or-less works with Asterisk and BLF (busy lamp field) that is worth sharing.

The description of the app, including screenshots is entirely in Japanese although the app's button labels and menus are all in English. Not sure why this is?

The app is "vPhone" and I found it by searching the App Store for "sip blf", it was the only result, so I gave it a shot.

So far I've worked out it can do the following:
  • 9 one touch dial buttons with BLF support - this is the killer feature for me!
  • Although it is after a short delay, it does support paging/intercom (personal killer feature #2)
  • A dedicated general call pickup option (hard-coded to dial **) (but it looks like it cannot do directed pickup)
  • Tell it the SSIDs of up to three WiFi networks to use - although this seems to be both a feature (selective connectivity so it doesn't attempt to register on other WiFi networks) and a limitation (I haven't yet found a way *not* to limit it to three WiFi SSIDs)
  • I haven't tested it yet, but it seems to support VPN tunnelling - not sure if it is its own implementation or using iOS' VPN implementation
  • It will pass dialled numbers to your phone's native dialler to call over cellular if your SIP connection isn't available (some others of course do this too)
  • Unlike, say Bria and Groundwire, ringtone options aren't all that cheesy. They suit my personal taste anyway.
  • I can't find any provisioning support, but for small deployments and home * boxes that's no biggie.

Most surprisingly, it's free, and does not have iAds.

I have a feeling the app is supposed to be just for the Japan App Store (at least for now) but accidentally released globally? Not sure. Found a good looking iPad SIP client ("TeliPad") featured on the vendor's website but cannot see it in the App Store.

I'll keep playing with it and report back as to reliability etc. Been playing around with it on two iPhones and an iPad hooked up to my * box, no problems found so far besides the call pickup limitation...