Parts of North Roe and Ollaberry were unable to make emergency calls in the early hours of this morning.
BT say the 999 service was down in both exchange areas, which affected 100 customers in North Roe and 150 at Ollaberry.
Around 60 customers at North Roe also lost their broadband service.
The outage began at around midnight and ended shortly before 9am when engineers re-routed traffic.
BT spokesman Mitch Reid said: “Investigations into the fault are continuing and we’d like to apologise for this break in service.”