You may have to ask them what modem they used as well as any 'accelerator' they use. There is that old PROPEL software that compresses on the server side but that is far too much to type about here in this small space.
56 kilobit (UNCOMPRESSED!!!) is the norm, what is supported and you will see multiples of that under the right circumstances with uncompressed data.
I'll stop here as only those that don't want to research this area will keep asking.