Is there a problem when using a temp table to generate your number ?

e.g.

create table #mytmptb (myNumber int identity(1,1))

set nocount on

declare @MyNumber int

insert into #mytmptb

output inserted.myNumber

default values

set @MyNumber = scope_identity()

delete from #mytmptb

print @MyNumber

Also keep in mind multiple processes may run in parallel ... locking may occur when using persistent objects or global temptb's.