Question : Add an extension to a Vonage line

I have a client who has two numbers on Vonage.  They have two Vonage boxes - on for each number (and one that also uses a Fax).  They have three phones, however and they wish to have two of those phones using one number.  Currently they are unplugging one phone and plugging in the other in order to use it (there's a reason for this, having to do with a rather expensive wireless headset on one of the phones). To complicate matters, the Vonage boxes are physically near the wireless router (naturally) and they want the third phone in an adjacent room.

My questions are these:

1.  Can I split a Vonage line using a standard phone line splitter?
2.  If I have to, can I put in a third Vonage device in the other room that would serve on the same number as the one near the router?
3.  If I have to use a third Vonage device, can that be plugged into a wireless bridge, rather than to run a line?

Basically, they have a long phone line that is running across the floor to the other room.  This is not the way to do things.  So I'm looking to either split the line and convince them to get a wiring guy to run a line from the Vonage device into the next room.  If they don't want to do that, then I will have to introduce a wireless bridge into the next room and connect it to a new Vonage device that would be programmed to use one of the existing numbers.  I suspect, however, that Vonage won't work that way.

Does any of this make sense?  VOIP is not my area...

Answer : Add an extension to a Vonage line

1 yes I put the vonage analog signal though the building on my old Pots lines including a splitter.
2 yes but to activate it with another VOIP number from vonage will cost
3 It's always better for call quality to wire the devices but why not suggest a 5.8 wireless phone set with 2 or more phones for the second and third ?