There is an asterisk bridge to skype - http://www.mhspot.com/sts/siptosis.html
but I don't use it.
I use skype through my computer to talk to other skype users - works great.
For actual phone I use http://voip.ms
through my asterisk box.
if you want voip gateways (use regular phones on your voip network) I have a bunch of mediatrix 1104s - http://www.voiplink.com/Mediatrix_11...atrix-1104.htm
and I think one 1124 - http://www.voiplink.com/Mediatrix_11...atrix-1124.htm
laying around that I'm not using - all used but work great.
As for voice quality - I've got Verizon FIOS - I've been running mega torrents at 1MB/Sec and above, streaming internet radio, and talking on the phone at the same time - no problem - never been an issue. SIP traffic (phone calls) is actually very tiny in terms of bandwidth. If you have some crap internet into your office you WILL have a problem - seen it before - echo and lag are the biggest issues.