Linux voip phone software

[TheIdeasMan]

Hi

Just wondering if anyone is using voip software on Linux that they have had success with?

I have already tried LinPhone, but it doesn't seem to like calling any phone at all.

In looking at the various options available, I notice that a lot of them use the SIP protocol - does that imply a restriction?

I am just after something that works, would like to call PSTN numbers and mobiles if possible :+)

Cheers

Edit:

Also wondering should I go down the asterisk road? Seems like a lot of work to write it.