- Runs on a Blackberry. In my experience Microsoft push email isn’t reliable enough and I am seriously thinking of changing back to RIM
 - Can call using any available network – wifi, GSM or 3G – deally can detect least cost route or allow you to set preferred network connection
 - Has the same inbound number as my work desktop phone so I can seamlessly take the same calls wherever I am – this realistically has to be a fixed line number as you have to be a mobile operator to do it otherwise.
 - Detects the presence status of my friends and allows me to send Instant Messages to any network.
 - Active directory lookup for corporate users to avoid having to store all the numbers locally.
 - High definition voice codec available for use on wide bandwidth connections (ie wifi)
 - High quality speakerphone.
 - Multiple VoIP subscriptions so that I can have both work and personal services on the same device.
 - Front and back facing video (I’m not sure whether I’m kidding myself here!)
 - All the usual touchscreen/music/GPS/integration with Twitter/Facebook and other social networking websites gadgetty stuff.
 - Unlimited battery life (hey – I did say ideal mobile VoIP client 🙂 )
 
If anyone wants to add to this list feel free to drop me a line or leave a comment.