What is the point of an API that you cannot access? They held a contest where they list alot of other companies that have VOIP apis. For instance, voxeo which provides a fully hosted IVR solution with free developer signup.
Until Sylantro offers the same it will not see wide adoption in the developer community and hence will notsee the kind of applications that could tip the market in their favor.
It is a shame that big companies only work with other big companies and do not open it up for developers.