When running this in SQL2005 I get the following response (after answering the question)
Msg 139, Level 15, State 1, Line 0
Cannot assign a default value to a local variable.
Msg 137, Level 15, State 2, Line 7
Must declare the scalar variable "@CustAccount".
You can not set the value of a variable at the same time as declaring it until SQL 2008.