I'm probably too late but I thought Id post anyway, just in case you haven't given up yet. Considering the amount of help you have received so far I'll be surprised if you ever return.
My advice would be to NOT use an arduino for this project, for several reasons:
- As a first project there is too much to learn in order to make an arduino perform this task; it would be like asking for instructions on changing the clutch in your car if you have zero auto repair/mechanical experience - it's too big a job for a beginner.
- I think it could be accomplished a lot easier without using an arduino.
I'll assume when you say "analog phone" you mean a legacy land-line telephone, like most people had in their homes 30 or 40 years ago. Those phones operated on a system that normally supplied 52vdc from the telephone company central office, and in order to make the phone ring the central office would send 85v AC down the line, on top of the 52vdc. The AC "ring voltage" was NOT 60Hz (60 cycles per second) like house electrical power; it was 20Hz, a much slower alternating current.
We don't need the 52vdc because all we really need the phone to do is ring. However, generating an 85vac 20Hz signal would be pretty difficult from a low voltage source, especially for a beginner, so I'm going to suggest you not bother. My advice would be to do something similar to what wvmarle suggested - using an mp3 player to play a phone ringing sound through a speaker you install in the phone. But I would not suggest using the "DFPlayer mini" that wvmarle talked about, as it's too complicated for a first-timer to learn to use.
Instead I would suggest buying a cheap mp3 player from ebay that has mechanical switches to operate it (not touch screens). Listing #253576477505 looks like it would work and it costs only 99ยข. See if you can figure out how to take apart the player and trigger it to play your phone ring mp3 tune using an external switch, which should be pretty easy, and if you can accomplish that task then continue with the project. If that turns out to be too difficult then you might want to reconsider doing this project, as it's going to get more difficult.
The cheap mp3 player will not drive a speaker with sufficient volume, so you will need to buy an audio amplifier as well, which again can be had on ebay for cheap. Listing 293001967969 is under $1 and has a volume control built-in. See if you can figure out how to wire the mp3 player to the amp and the amp to a small speaker. This will give you more experience with wiring and electronics, and once you accomplish that task the rest will get easier.
Now if you add a second song to the mp3 player (your audio message) you should be able to wire the telephone hook switch to trigger the "next song" function on the mp3 player when the receiver is picked up. You might also need to switch the speaker output of the amplifier from the speaker you mounted inside the phone (for the ring sound) to a speaker mounted inside the ear piece part of the hand set. If I remember right, old desk-top analog phones had multiple contacts on the hook switch so you might be able to use one set to trigger the "next song" and another set to change speakers. If there is only one set of switch contacts you will need to use that switch to power a relay that has multiple contacts.
I'm sure you will run into some hiccups along the way that I have not thought of, but that's always the case with electronic projects and it can be challenging as well as frustrating. But solving those problems can be a rewarding experience so I encourage you not to give up too easily. This is a do-able project, and I can see some fun practical jokes in your future.