Is it necessary to wean off atenolol 75mg? Am switching to verapamil sr 120mg. Was advised that no wean is necessary. Stop atenolol, start verapamil?

Depends. The worry about not weaning off atenolol 75 is that you can develop reflex tachycardia (rapid heartbeat) - the rationale in your case is that the verapamil should counter this making it unnecessary to wean.