I was wondering about that, it is described as:

"where rather than hold the data, it is split in two so CertiVox has one half and the user has the other, and law enforcement would need both to access the data."

By data here, do they mean encryption key? If so then I'm not sure what splitting it in two does as you presumably have to join them together somewhere and GCHQ would presumably just attack wherever the complete key is available.

[Edit: Product details here, it appears to be Open Source: http://www.certivox.com/m-pin/]