I need to have a second BT line installed for work (they are payin).... Is it possible to do this but just have one set of DECT phones which will tell me which line an incoming call is on and also let me select from the 2 lines when calling out ?

there is one phone system I know of and that is the BT Airway phone system. BT airway

Nearly £700 and they can't even spell separate!

Can't most DECT phones be paired with more than one Base station ?

Yes, you can register most DECT phones to 4 base stations. You can then change to whichever you like...

Can you register to two base stations at the same time?

I'm afriad not!

So what we are saying then is that I'll need 2 base stations (one for each line) but the handsets will be transferrable between the 2.

Thye may be transferable, but with they ring when either incoming line has a call, or only when the one that they are currently registered with has.

Only ring when a call is received on the currently registered base station.

Unfortunatley, what you want to do is going to cost you quite a bit as effectively you need a switchboard with DECT capability. If you can cope with wired phones then you should be able to pick up a small switchboard unit for no more than £200

I've had Airway for about 8 years now, would of thought there was something better and cheaper out there by now

Get a BT Broadband Talk line?

With most VOIP adapters you can have 2 numbers setup, some will allow 2 numbers on the same phone or the same incoming numbers at different locations.