IB takes very little bandwidth.. In fact most internet software takes little bandwidth. I did use a 33.6 dial up [much more stable than 56K depending on modem/ISP compatibility] to IB, eSignal and later QCharts and chat etc... no problemo.
IB does not use level II [many level II active at the same time can take more of the pipe].
It is easy to check, when you have a modem it is possible to check how many bytes are received per second. Trading software usually takes less than 1.5KB per sec [average is more like 0.8 in the setup I described] which is very confortable with dial up.
People do not usually realize that 33.6 or 56 is a lot of data per sec and quotes easily compress too [automatically through the modem].
So yes, you can do it that way, dial up that is. You will miss the speed for web surfing of course !
Now I have a cable access and lucky I must be almost alone on my node here !

So I use the extra pipe for voice chat to friend traders.
I must point out that the real advantage of Cable or ADSL is the permanent connection. The fact that you can hardly loose the connection. Depending on your dial up ISP, you may experience poor stability and that's bad.
This is why my 56 modem was used only in 33.6 mode [much more reliable on the wire and with the ISP I had].
But if you have a stable dial up connection [never interrupted for 8 hours or more], then speed is no issue for trading. In fact, I have also noticed broadband connection sometime suffer many 'hops' on the route to the destination, resulting in small delays [milliseconds] while, the good old dial up would use a more direct internet route without these delays [without the speed of course].
vpiNeo