If this is a line off a VG224 or similar, in Call Manager, click Device / Gateway / the VG224 in question / select the port this line appears on.
Click on the line, scroll down to "forward all". Enter the full number in the space including outside access (ie 9) then enter the correct calling search space entry for off site calls. You may need to enter Device information directly below that. This should give off site forwarding.