asterisk users - Jul 2005 - How to use Audiocodes MP-108 with Asterisk in Singapore

I am currently installing an Audiocodes MP-108 with Asterisk in Singapore.
I am able to make outgoing calls but incomming calls just get cut by the
MP-108
I can see the corrosponding frontpanel led light p but the call gets cut so
I'm very confused about what could be wrong.
                                                                                
Could this problem have something to do with this being a Singapore Phone
system and MP108 designed to work only with american phone systems.
                                                                                
any help will be apreciated.
                                                                                
thanks

-- 
regards
Vikram