OK, SIP sounds good, is there an adapter like the one I was looking at that uses SIP, and Linux?
Yes there are lots of SIP ATAs.
They generally plug into a LAN router port.
They are OS agnostic, requiring a browser to set them up.
After that they work without the PC.
The same info is entered into them that would be entered into a PC client like Ekiga or Linphone or Twinkle etc.
Most providers will supply details on their site and even give example of different hardware setups.
I suggest you read through some of the hits you get from Google using
as the search term.
It is noticeable that Skype will be shown here at the top of any search using SIP ....... even though it does not use the Protocol! The power of money I guess.
You do need to be aware that SIP and Skype are separate.
If you wish to call people using Skype then you need a Skype setup.
If you wish to call people using SIP then you need a SIP setup.
There are some companies now, for a fee, which manage cross protocol calling. They are few and far between ... Gizmo being one.
An example of a hardware page from a VOIP providerhttp://www.blueface.ie/helpandadvice/specification.aspx
This is just an example from my provider. You will find similar providers in your locality with local prices etc etc.