UDF returning a Boolean

Can a UDF return a Boolean value? I am taking my first stab at making a UDF for SQL (after successfully writing my first stored procedure). This function would wrap up a service program procedure that returns an indicator. It looks like I might have to make the return value CHAR and check for '1' to see if the UDF is returning a 'true' value. Since SQL can handle Boolean (e.g. where exists), I was hoping the UDF could return such a value so I wouldn't need the actual SQL to say = '1'.

For example:

Want to do:
Select *

From callrecords

Where isTollFree( ANI )

Worried I might have to do:
Select *

From callrecords

Where isTollFree( ANI ) = '1'

I didn't have any luck in my own search, so I was hoping someone might be able to chime in. I'm at IBM i 7.1

Thanks,
Kurt Anderson
Sr. Programmer/Analyst
CustomCall Data Systems