Sending data through a telephone line

I would like to use an arduino as a Line telephone and to send data, I will use the RJ11 connector
These are my questions:
How do I make the phone in general?
How do I produce DTMF?
Would I need to add protection to the Arduino?

Thanks in advance.

Check with your local telecoms operator, with respect to attaching hobby electronics to their equipment

Check this out: www.cermetek.com/catalog/telephone-line-interface/datasheet/xe0068dtrevc.pdf

FCC Registered DAA Module with DTMF Transmitter/Decoder

FISHY_ROM_HACKS:
I would like to use an arduino as a Line telephone and to send data, I will use the RJ11 connector

In most places in the World, you can only connect approved equipment to the telephone systems.

And for good reason, to protect the telephone equipment and exchanges from damage and for the safety of engineers who may be working on the lines.

You could use a 56k modem, connected by RS232 to your Arduino.

There must be millions of redundant 56k modems available.

For generating DTMF, see Arduino Playground - DTMF
Apart from the regulatory aspects, you have to know what you are doing when you design a device to interface with a land line telephone. For example, during ringing of your own phone, around 90 volts RMS AC can appear on the line. See here for interfacing guides: http://www.rane.com/note150.html or also here: link .