Chinoy, please be assured I try to answer every question on the IVM, Express Talk and Axon forums that I can. If I do not answer the question it is because I have no solution or suggestion or experience with the topic OR I am still researching the topic and trying to come up with a plausible solution.
As for your MySQL plugin question, I've never used it and I don't have much MySQL experience so I'm not really able to help much there.
Your other question involves a problem I have yet to encounter, so I am unable to provide much expertise. From my experience with VoIP in general is that if one of the parties forces a codec that the other party's phone/softphone is not compatible with, as soon as the phone is picked up the call disconnects.. however in your case this does not make sense since IVM and Express Talk use the same codecs and are fully compatible. I thought it could be a port forwarding issue, but that usually just leads to a loss of sound, not an actual disconnection of the line as soon as the call is picked up.