Note that a kind of sender-pays is already used in practice as all big content providers pay for CDN on a per GB basis, and the CDN company in turn pays for bandwidth.
However, the ITU would like to charge across many networks and discriminate based on the type of service provided.
So if data from your network A reaches the customer through networks B, C and finally D, then D would like to charge you to deliver it and not slow down things artificially.