The following is what you are looking for:
SELECT CASE WHEN ExitReason = 7
THEN 1
ELSE 0
END AS CallsAbandoned
FROM queuecall
Or if you are wanting a count of the result of the CASE then try the following:
SELECT SUM(CASE WHEN ExitReason = 7
THEN 1
ELSE 0
END) AS CallsAbandoned
FROM queuecall