I am a physical keyboard device user, first and foremost, though I did enjoy using the BlackBerry Z30 for a while, until going back to the BlackBerry Q10 and now the BlackBerry Passport. The only problem with a physical keyboard is the noise it makes. I like the noise, don't get my wrong. That clicky sound and tactile feedback is why I love it but there are just some situations where that clicky sound isn't appropriate. Like when you're in a very quiet class and you want to send a BBM or Tweet, it can be quite distracting. That's when Silent Keys comes in handy.
Silent Keys is an app that allows you to type with a virtual keyboard. You even have a dark and bright to choose from as well as keyboard style and size. You can even adjust the padding on each side of the virtual keyboard -- one handed use anyone? There are also many languages to choose from too, which some people have found to be very useful and handy. All these options can be found in the app Settings.
To use the app, you can open up the actual app, starting typing in silence and then share the text to an app. Or you can invoke it from whichever app you are in. To do this you just tap and hold on any of the text within the chat you're and then tap Share. Choose Silent Keys from the list and this will bring up Silent Keys keyboard. Type out what you want, then hit Copy Text and this will bring you back to where you were.
The only thing with the Silent Keys keyboard is that it doesn't auto correct spelling. This hasn't been too much of a problem for me though. I have been using it with the BlackBerry Passport and the big screen doesn't make things too cramp. Silent Keys is available for all the physical keyboard BlackBerry 10 smartphones - Passport, Q10, Q5, P'9983 and the Classic. As I've said, I have only used it with the Passport so the big screen makes it nice to use. Not sure you would get the same experience on smaller screens. However, I do find it to be a pretty useful app.
If you're interested, Silent Keys costs $0.99.