I have built GNU Radio blocks to encode and decode DStar. These blocks use NWDigitalRadio's ThumbDV for the vocoding. My OOT (out-of-tree) module is at https://github.com/ac2ie/gr-ambe3000.

The DStar Decoding block is mostly complete. The decoder prints any incoming header as well as any "slow data" in the voice frames. (Of course the main output of the decode block is the audio stream!) A GNU Radio flow-graph for a DStar receiver is included. (See the picture below.)

Encoding is still a "work-in-progress". Output of my current DStar Encoder block does not have the prepended 660-bit frame header and frame sync. The output is also not properly terminated with a terminating sync flag. In spite of these shortcomings, a flow graph is included that will transmit a valid voice stream that can be successfully received with a DStar receiver, it just won't have a header or a terminating flag. I'm still working on the details of how to implement that in GNU Radio.