My advice would be to stay away from Skype. I am currently using it and I'm not happy with it. It cuts out occassionally.
Some of that may be attributed to my setup here however my other irk is calls get missed on my skypein number and I know for certain that is Skype's end with the problem.
I also think that SIP based phones are the go for business as that's what all the real phone people use.
I also tried 3CX, it's a great peice of software but it was too much mucking around in my opinion.
I'm about to try mynetfone's virtual pbx with SNOM IP phones, might work...might not
