Shishir,
you mentioned that too many calls are hitting unit. This can be a bad thing. You should make sure that no more than 24 calls are going to the unit. After that, if no calls are going through, it might be a config issue. Check your HND settings to make sure that you have matching patterns and then do a quick test on each line for dialtone.
MikeM
mike_voip@hotmail.com