There are three bands that go by the name Callahan.
(1)A metal band from Vancouver.
http://www.myspace.com/callahanband
(2)A pop-punk band from Springfield,Ohio.
Myspace: myspace.com/thislove
Now with new members and re-named This Love
(3)An instrumental pop band from Perú.
The official site is www.callahan.sugarpop.org