Case In Inner Join? SQL Statement Help!!

Hi,

I have a 2 different telephone number tables,

Table 1 has some numbers beginning with '0' i.e. 08001234567 and some without the '0' i.e 8001234567



on my Table2 i only have numbers starting with '0' i.e 08001234567.



I would like to make a INNER JOIN statement and check if the telephone number dont have a starting '0', then append to it and try to do the join so I get both set of data.



for example (this doesnt work however...):

SELECT *

FROM dbo.Calls INNER JOIN
ON

CASE WHEN SUBSTRING(dbo.CallData.TelephoneNumber, 0, 1) = '0'

THEN dbo.Calls.TelephoneNumber = dbo.Post.TelephoneNumber

ELSE '0' & dbo.Calls.TelephoneNumber = dbo.Post.TelephoneNumber <--append a 0 at the start

END CASE

AND dbo.Products.FK_Client = dbo.CallDataSets.FK_Client
GROUP BY dbo.CallDataSets.FK_Client



I hope you understand what I am trying to achieve here...

Any help is appreciated!



Many thanks,

Jon