It is technically possible to use a pound key (#) as an end of input indicator. It is almost impossible to change the users habits though, not mentioning the ne

It is technically possible to use a pound key (#) as an end of input indicator. It is almost impossible to change the users habits though, not mentioning the need to reprogram thousands of telephony switches. Another (better) option here is packet sending of DTMF string - digits are collected on a smart user's device (i.e. iphone) and the complete number is sent as a digit string, not one by one. Problem here is that there are still lots of dumb phones that don’t do that. Analog lines (copper fxo/fxs interfaces) are also present even nowadays. So as usual, legacy and backwards compatibility are holding back progress.