Phone sockets/lines

[#1]

Just about to start moving into a new house. I've found two "sockets" in rooms downstairs, and one upstairs as well as an extension downstairs that ends in an ADSL type plug. It looks like there's a cable from outside going to both of the sockets downstairs, one has a new BT OR (grey writing) faceplate, the other has an old style all white socket with raise BT logo. How do I tell which is live, or whether the property has two lines? I've yet to get a phone/bb service connected to the property but will do shortly.

[#2]

Plug a phone in to a socket and listen for a dial tone? If you have one, dial 17070 for the line number. Repeat for other sockets.
Phil

[#3]

@pg I salute you sir 

[#4]

Will there be a dial tone even if I havn't got a line rental agreement in place?

[#5]

It's a distinct possibility depending on how long the line has been out of use.