This trigger is supposed to change the phone number to all 1s if the first 3 numbers in the phone falls in the IN criteria. It's not doing that, instead it doesn't and also if the phone number is null, it updates that with all 1s also which is an undesired result
ALTER Trigger [IT_Restrict_AreaCodes]
ON [dbo].[DialEmpty]
AFTER INSERT
AS
if @@rowcount = 0 return
Update d set phonenum = '1111111111'
From dialempty d join inserted i on d.DialID = i.DialID
inner join project p on p.projectid = i.projectid
Where Left (i.phonenum,3) IN (203,475,860,959,406,218,320,507,612,651,763,952)
AND p.projecttype = 6