Automatic transcription software for phone audio recordings

Please recommend software to transcribe audio recording of telephone calls. The software needs to perform the transcriptions automatically, and not depend on a human to perform the transcriptions.

The transcriptions do not need to happen in real-time; we can assume the telephone calls are all pre-recorded.

All calls are in the English language. A single person is one of the parties in each of the calls, and that person can provide voice training samples, if needed. The other party varies in each call, and voice training samples are not available for them.

The calls were recorded in compliance with applicable laws, and privacy needs to be maintained; thus online services will not be appropriate.

Here are the requirements:

1. Android or Windows (any versions)
2. Just needs to provide a general idea of the conversation. Does not need to be perfect.
3. Output of sequences of recognized words is sufficient. Does not need to support punctuation.
4. Closed-source or open-source is fine. Open-source is preferred, but either is acceptable.
5. Gratis (free of cost) is better, but up to about 40 euros/dollars is fine.
6. Must not require transmitting the recordings over the internet.