Variety of different companies doing gateways etc...
Pika Technologies: http://www.pikatechnologies.com/
Chanskype: http://www.chanskype.com/
(Resource hog...developers answer your questions about once every 7 days...found it buggy...didn't want to hangup skype calls etc...asterisk would hangup...skype call would continue)PsGW: http://www.rsdevs.com
Vosky: http://www.vosky.com
Skype Gateways: (Voip-info wiki)
http://www.voip-info.org/wiki-Skype+Gatewaysetc...etc... find all kinds of asnwers to your questions searching skype and asterisk in google...some of which suck, some are ok, some are too costly for what you receive in return. For instance I say a gateway some company was trying to sell for 20k that did 8 channels ROFLMAO...so there are obviously some crackhead companies out there too.
So far I think Pika, chanskype, PsGW, and the gateways by Vosky are the most well known.
I will say that the call quality in chanskype though was no different than doing a direct skype call...and supposedly they have updated the channel driver to fix some of the bugs I was experiencing...now if they actually answered a question in less than 7 days...they would probably sell a lot more licenses.