AT&T says 911 emergency telephone service has been restored following a power issue that disrupted the service in some parts of Oklahoma.    The telephone company says 911 service was disrupted Wednesday morning in Enid, Shawnee and some other emergency call centers in the state. Affected centers rerouted calls and technicians quickly resolved the problem after isolating the power issue.    Call routing was affected for about two hours beginning shortly after 10 a.m. Service was restored by 12:15 p.m. AT&T says it's still investigating the cause of the outage, which involved a power issue at a facility in the Oklahoma City area.    Enid Police Department Capt. Jack Morris says the outage affected the 911 system that serves Enid as well as Garfield and Major counties in parts of north-central Oklahoma.