This is not something new, DTMF decoding has been around for awhile and a little to late for us to take advantage as most people push to call a someone rather than typing it out.
It works quite well providing there is not too much background noise going on. There is a setting that allows you to compensate if you are not testing it out under ideal conditions.
See it in action here (video is quite poor and doesn't do it justice). Probably the best DTMF decoder in the app store, but don't take my word for it. Have a look at alternative and possibly free DTMF decoders in the App Store.