Hi, if a person has cable internet with a regular landline, would they also be able to sign up to a VoIP provider as well? Reason I am asking is that they will be sharing the broadband with the next door neighbor via a wireless extender and the next door neighbor was thinking of getting a separate landline and I was suggesting VoIP for them.
Would they also be able to plug the ATA into the wireless extender too?
VOIP will work over any decent internet connection, no worries there.
Not sure about the wireless extender, do you mean a wireless->wireless extender? Because I would guess not then, though I have never used one so cant say for sure. If it's another router connected to ethernet, providing the same network, then yes, you can plug the ATA into it.
As long as the internet connection has enough bandwidth you will be able to have as many VOIP lines as you want.
I had a setup last year that my flat had internet coming from the landlords house about a KM away and had a 2Talk VOIP line running through a SPA2102 for our phone line, it worked without much problems unless someone was doing alot of downloading.