I very much want to respect the rules of the forum, but Iím not sure how this reply will fit with this, but here goes.
There are many ways of providing bonded connections, and different companies will ďbondĒ in different ways.
One way of doing this, and forgive me if this is starting to get technical, is to provision multiple ADSL (or FTTC, Ethernet, EFM etc.) lines, which do of course each have their own IP address. But the customer would never see these addresses, or frankly care about them, because they would be connecting their firewall up to a bonded internet gateway, which would sit in front of each of the network termination endpoints.
The IP range we mention would be the IP range on the bonded internet gateway, which is indeed spread across all of the component circuits (tunnelled to a central bonding instance).
Complex algorithms ensure that when a tunnel drops on an individual circuit, traffic would continue to and from the same IP range across the remaining lines, and remain transparent to the end user and their firewall.
I hope this clarifies.