MarketPress Gateways

Hi,
My client has employed telecoms company to run the Gateway for the website i'm building. For this to work they're asking me to make MarketPress:

» POST a URN to our server
» accept a serverside post from our server and reply with the user's details and the transaction amount
» Accept a serverside post from our server and update the order status based on the URN passed.

Is this something MarketPress can do? Are they making this process more complicated than it needs to be?

Help would be appreciated. Thanks.
Neil