I have successfully used Set CallerID with SIP/IAX2 with relevant PSTN providers. What I have not done is tried this with a Zaptel channel connected to the PSTN as would appear to work based on this:
voip-info.org/wiki/view/Setting+Callerid
Does anyone have any direct experience on getting this to work? Any recommendations/gotchas?
Note - This is for legitimate purposes.