More a ‘proof of concept’ and certainly a very (very) complicated workaround but appears that using Skype on your iPhone (which it seems that 1 in 3 American’s want – the iPhone not Skype on the iPhone that is) is becoming more of a possibility:
“The Skype-on-iPhone solution is described as a “workaround-around” using a remote control application, SoonR, to remotely use the Skype application running on the user’s desktop computer, and make the calls from there.
It’s a bit more complicated than that, however.
SoonR Talk is an AJAX application running on the Opera browser (which has to be installed on the iPhone). It connects to the desktop via the SoonR server, and then SoonR Talk sets up the call.
It dials out from Skype and makes a SkypeOut call to the mobile, conferencing the two calls together. This uses at least one and possibly two paid SkypeOut calls, which in many cases may still be substantially cheaper than dialling direct from the iPhone. For instance, unlimited SkypeOut credits for dialling can be bought for $30 per year.” Macworld