I am not happy with these people. I held an account unused for several months with them for a client. When the client was ready to get online, they told us that they don't hook up with modems connected to digital phone services. There is absolutely nothing in their advertising which admits such a limitation. When I asked for my money back, and for technical details of their problem, they did not answer my email. In the background here is the following:

digital voice networks have become the norm in U.S. urban areas

if you are on an analog network using a phone made before the
introduction of digital networks, you of course can
communicate with phones calling you from a digital service.
basicisp knows this, and thus I find it hard to believe they
are being honest with me, especially because they
refuse to discuss the technical details of their supposed
problem with digital networks.