The most popular electronic anti-stuttering devices provide delayed auditory feedback (DAF) or frequency-shifting auditory feedback (FAF). The stutterer hears his voice in headphones delayed slightly or shifted in pitch. DAF and FAF reduce stuttering without training, mental effort, or slow or abnormal-sounding speech. But the beneficial effects dont last long unfortunately. Most people stop using it in  1-2 months, for following reason:

1. It picks up the other sounds from environment (the converstaionla partner) and plays that too in your ear with delay.. This becomes very confusing (sometime painful) in a noisy atmosphere.

2. It does not help with silent blocks or hesitation.

3. It does not do anything for the emotional or coginitive issues from which PWS suffer (90% of the iceberg)

4. You develop a dependency and feel lost when you dont have DAF with you, or if it stops functioning for some reason.

5. Brain adapts and gets used to DAF effect in a few weeks to months, and then, stammering returns.

If you just want to experiment with the idea, you can download free software, install it on computer/ laptop and use it with a headphone.

http://www.speechmonitor.org/

A similar program, installed on cell-phone, with bluetooth headset, can give you same functionality- at little or no cost:

http://www.artefactsoft.com/pocketdaf.htm

http://www.fluencypal.com/

But remember, communication is more than fluency- and as such has to be learned and practiced in real life situations, without electronic crutches, for best and lasting results.