[Asterisk-Users] Play tone till first digit read

[Ed Greenberg]

I'd like to collect digits (either a fixed number of digits or a variable 
number ended by a pound sign.  Read() is perfect. Authenticate is pretty 
good too.

What I need is to prompt, not with a recording, but by playing a tone that 
will terminate at the receipt of the first digit, sort of like dial tone. 
In fact, it could BE dial tone.

Anybody know how to do this?