The first function recursively removes all characters matching a supplied patindex patten on a string by string basis. 

select cusno,last_name,[dbo].[xRemoveMatchedCharacters](last_name,'%[^0-9a-z]%')

 from cusmas c

select cusno,last_name,[dbo].[xRemoveMatchedCharacters](last_name,'%[0-9a-z]%')

 from cusmas c

The second version is a table based function built on the first function.

select cusno,last_name,z.*

 from cusmas c

 cross apply [dbo].[zRemoveMatchedCharacters](last_name,'%[^0-9a-z]%')z

select cusno,last_name,z.*

 from cusmas c

 cross apply [dbo].[zRemoveMatchedCharacters](last_name,'%[0-9a-z]%')z