I want to build a test circuit that will enable me to detect when a phone
goes off-hook and detect the DTMF tones thru a modem.

I was told to use the following circuit:

(please enlarge your screen to display it)

 phone

 |      |
 |      |
 |
+--------------o-----------o--------------------------------------------o---
----------------o
 |                     |           |
|                   |
 |                     |           |
|                   |
 |                    +-+          |
+-+                  |
 |                    | | R=100K   |
| |                  |
 |                    | |          |
| |R=1K              |
 |                    +-+          |
+-+                  |
 |                     |           |
|                   |
 |   R=1K              |           |
|                   |
 |   +-----+           |       +|\ | 741       1N4148   1N4148
/                   |
 o---|     |----o---------------| \|+          |\|       |\|      +-----+
|/                  ----- 12V
 |   +-----+    |      |        |  \-----------| |-------| |------|
|-----|  2N2222A           ---
 |              |      |        |  /           |/|       |/|      +-----+
|                     |
 |              |      O--------| /|-                             R=10K
>                    |
 |              |      |       -|/ |
\                   |
 |             + +     |           |
o---o hook          |
 |        R=560| |     |           |
|     detect        |
 |        ohm  | |    +-+          |
+-+                  |
 |             | |    | | R=10K    |
| |R=560ohm          |
 |             +-+    | |          |
| |                  |
 |              |     +-+          |
+-+                  |
 |              |      |           |
|                   |
 |
+-------o------o-----------o--------------------------------------------o---
----------------o
 |      |
 |      |

 modem


 I know very little about telephone circuits:

 1. will it work ?
 2. can I lower the voltage, say to 9V ?
 3. is there a better circuit ?


 Thank you

 Duilio Foschi