Regaring Exchange IM

Hi,
I am workign in a software develepoment organisation. we are using exchange IM for the out internal communication . From past few months, we are facing Fluctuation in Exchange IM very often.
I checked up the domain contraollers and smtp servers i for any errors in event logs but couldn’t find any errors regarding this issue.

Can any one helpme in this issue ASAP.

Apart from exchange IM , is there any other enterprise quality hosted solution for IM?

Thanks In Advance ..

Sushil