Had this phone for 9 months now. Tweaked things and discovered things that aren't in the manual. You can set 6 voip operators, if you have several incoming voip numbers you could assign them for use by different users so that when the phone rings is states who the call is for. Have managed to figure out how to dial via different voip providers without having to go to the PC first, set up the providers from the web config then append each number with #1 for provider 1, #2 for provider 2 etc etc, or simply set up dial plans via voxalot.com. There's simply no other phone out there that provides you with the options that the S450IP does, you can even combine it with the M34 USB adapter and use it for sykpe as well.

Fantastic phone. Fantastic service from Ligo.
Functionality of the phone is spot on, although it does feel plasticy in construction and very lightweight, so only time will test how good it really is. VOIP quality is amazing (I use sipgate.co.uk) - just as good as my BT line in fact. You need to be fairly technical to set one of these up as the manual is pretty poor, as is the Siemens website. You have to just try things out and you get there in the end! All in all, I am very pleased and will be ordering extra handsets (assuming Ligo start to stock them! hint hint!).
4 starts only as the user inteface on the phone could be much better and the build slightly heavier, but if you want a great IP phone that does landline calls as well, I don't think there is anything better at the moment.