I have a query that finds duplicate customers using the same credit card:

select iproductid,caccount,count(caccount) as cnt  
from customer c
group by iproductid,caccount
having count(caccount)>2
order by iproductid,cnt

This gives me results like

iproductid  caccount                       cnt         
----------- ------------------------------ ----------- 
1           xxx                            3
1           yyy                            3

Now I want another column that tells me "of those customers using the same credit card, how many have the same last name?"

I probably could do it with cursors and maybe a UDF, but is there another way using the select? When I try I correlated subquery, I can't get the number of records to be returned to me.
TIA