how to fix caller id mh9915bk?

Either your phone is not compatible, or there is a small fault n the line somewhere.

Possibly rectified loop, normally to do with a damp connection or socket.
You may want to get BT to do a line test for you, or you can test your line on there website, assuming you have a BT line.

But be careful as if the fault is in your home somewhere you may be in for a big call out charge.

Andy - BT Engineer
December 2009