Hello Mr. Sriharsha Vedurmudi,

You wrote:
By the way, the motherboard of the system contains P80C32UBPN and MT8981DE chips. The first one, Philips, is the mC for sure I know, but what is the second one?

You can find a data sheet on this digital switch from Mitel at the following web site. http://www.gaw.ru/doc/Mitel/MT8981D.PDF

It sounds to me this project is from a bunch of cheapo's, be very careful. Most companies would cuss about the expense of upgrading but they would pay it. Be wary of after the sale support these people might expect. Although you might be hungry for the job it might turn out to be NOT worth what you will get paid for it.

Regards,

Charles Bannister