Wire landphone speaker to arduino (noise problem)
Only to add something important to comments: The phone landline comes to you from quite far away. The distance between your phone and the telephone exchange can be several hundred meters, even kilometers in the rural areas. There can be a substantial voltage between the phone line and any equipment in your house. 

The phoneline has a constant 50....100 VDC for supplying the phone and sensing what's up (dial, open, open a call, close a call). Onto that is added 50....100 VAC as the ringing when somebody calls. During a call tde DC is still present and the speech is about one volt AC on it. You must have a proper isolation and filtering circuit to separate the components. The proper circuit is defined in general telecommunication equipment regulations and they must be considered as the law.

The noise: probably you have not sniffed more than a faint smell of what is possible. The 1000 volts surge will come some other day. Your phone has a thick insulation for that reason. Answering machines, faxes, modems etc... must not have any galvanic contact to the phone line, all connections must be done through isolation transformers, optocouplers and relays. Otherwise - sooner or later the smoke puffs out. It can well happen in the telephone exchange, too. Remember: they will have no difficulties in following the line and dropping a hefty bill, even a lawsuit to you.

A quidance: Do not connect anything homemade to the phoneline until you can obey the technical circuit regulations exactly. Rather pick the stray fields by a telephone signal picking coil or use a microphone. Add an amplifier, ADC the signal and detect the different events by software. No need even to buy a mic, the speaker in your image is ok.

Proper telephone landline interfaces for modems, telefaxes etc. are available as modules - no need for discrete relays or transformers. They also handle the audio signal and convert between 4 wire (=separate audio in &amp; out) and the bidirectional 2 wire phone line. Here's an example:

http://www.cermetek.com/catalog/telephone-line-interface/datasheet/ch1817_607-0007.pdf

See other discussions of the same topic - how to connect Arduino to a landline.