Yes, pay for
n lines. I have four lines. The charging scheme I have chosen is where I pay a certain small amount for a copper line and then a certain amount for fownllad traffic according to how much download I need. Adding another line is about £30 pm can’t remember about VAT and line rental. I pay line rental included anyway (not separately to BT).
My ISP handles the downstream splitting of traffic and my router, a Firebrick FB2900, handles the upstream splitting. My lines are not all equal speed, so the traffic is split in the right fraction according to each line’s capabilities. That way you just have a single IP address and everything works at multiple speed. It’s also the cheapest way of doing it, or can be at least, as I pay just a small amount for each copper line and I have a lot of lines yet I pay only once for traffic, not
n times over. This is the zero hassle route.
If you choose use two different ISPs, a router on the internet would be needed to handle the traffic splitting; without such a ‘remote’ router you would have several IP addresses at your end and single downloads would not go any faster although with multiple downloads in progress then you would see the speed benefit, but overall the value of such a system would be much more limited. If you use a capable ISP, then everything is done for you;
without this, if you want fully effective bonding, then you would need to do things yourself and either park your
own traffic-splitting router on the internet or you can
rent the use of one from Andrews and Arnold for example.