Call-by-IMSI got to be supported by BTS, which is not normally the case, however
OpenBTS fork from Fairwaves have testcall function which does just that.
In general - mobile-terminated call can "by IMSI" because for mobile phone
there's no
difference in how it was reached exactly_ as long as BTS exposes that functionlity.
For mobile originated calls I think it can be implemented on BTS side if you simply
use IMSI as a phone number in authentication db/sip backend of OpenBTS.
--
best regards,
Max,
http://fairwaves.ru