by compressing data, removing pop-ups and and removing advertising from web pages before delivery. They also convert all Gifs to Jpegs on their servers. If you don't mind your surfing experience being customised in this way you may see a performance improvement. You'll also see web pages that are slightly different to the ones everyone else sees.
There's no way that Proxyconn or anyone else can increase the amount of data that passes down a copper phone line in analogue form in a given time, and you must bear that in mind. You will almost certainly see some improvement if you use Proxyconn, but it may not be anything like the 5x improvement figure they quote as possible, and will very much depend on line conditions (and internet traffic) at the time. My personal view of such technologies is that if they worked as well as some of the claims made for them everyone would be using them.