HamQTH's API is pretty easy to use and provides a decent international callbook.
http://hamqth.com/developers.php
I use it for validation and profile at http://hf.dstar-relay.net and http://qso.freedv.org
If someone wanted to write a simple callsign lookup, it wouldn't be a big deal.
------------------------------ John D. Hays K7VE PO Box 1223, Edmonds, WA 98020-1223 http://k7ve.org/blog http://twitter.com/#!/john_hays http://www.facebook.com/john.d.hays