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how can i make a connection between gsm phone and DTMF decoder?

I've seen the project cell phone operated robot and i'm enthusiastic to do it.
(link : https://www.instructables.com/id/Cellphone_operated_Robot/)

i have a motorla l6 phone with me and i'm planning to use that in the circuit. It has auto-answer option. But it has an USB port to connect the headset. If i want to use it, is it ok if cut one of the ear phones and connect the wire at the 2nd pin of DTMF IC?
The next thing is what is the significance of word "RING" written at the ground in the circuit (left side at the bottom)

Picture of how can i make a connection between gsm phone and DTMF decoder?
110100101108 years ago
ring = +

tip = -

its the names of wires in phone line

since there is a capacitor on the wire i think that they can be swapped (+ - dont matter)

the chip seems to be intended to work on phone line voltages. it may require amplifier / tiny step up transformer to work with the low voltage of the cell phone