As part of a system we are trying to design we want to be able to make numerous calls to Skype phones. Is this possible without getting lots of “SkypeIn” numbers? Can SIP somehow be “translated” into whatever protocol Skype uses?
In short: not now 
This is a limitation of Skype, not Asterisk. As Asterisk may interconnect with LibJingle (Google Talk) in v1.4 about to be released.
It’s on the way 
Some have asked about interfacing Asterisk with Skype, and the normal answer seems to be “can’t be done” (due to Skype’s proprietary and closed protocols).
I had a thought about that, and as a rank newbie in Asterisk use and configuration I have no idea (yet) how to make this work, but it seems to me…
Aren’t there devices out there that allow normal analog phones to become Skype phones? I assume that they must convert a modular phone plug to USB, so that you end up plugging your plain old analog phone into your USB port.
So, why not just jumper the modular end of that adapter over to an FXO port on a Digium Asterisk card, on the same or another computer that is running Asterisk?
Theni it would seem to me that the only thing remaining to do would be to figure out a way to structure the Asterisk dialplan so that it is able to select from the Skype list of contacts. Anybody here know how to do that?
Asterisk dialplans could also be structured to make SkypeOut calls to regular phone numbers; all that is needed there is to figure out a way to prepend the phone number with a plus sign (+). On the Radio Shack and Linksys Skype phones I have, that is done by holding down the zero key for a couple of seconds. Anybody know how to do THAT with Asterisk?
holding 0 tells the phone to make a +, I doubt holding 0 on a normal phone would do the trick…
but if you want a really long 0 dtmf, just make a sound file of it and playback() it…