What do you think is the best way to start this project ?
Jay, congratulations: you have managed to ask the most important question, first. Aspiring engineers 2x or 3x your age often fail in this regard. The best way to start is to:
1. Document what you want to do
2. Research what others have done
3. Go back to #1 and rewrite it in more detail - an outline is a good way
4. Go back to #2 and collect specific implementation ideas/code/examples/notes
5. Build a prototype and incorporate your own code
6. Debug the prototype
7. Compare #6 with #1 - are you happy?
8. If YES, you are done. If NO, rewrite #1 or continue with #5.
I'm thinking in using two Arduinos (one in the base and the other in the phone) and be able to communicate with each other via rf.
replicate a normal cordless phone using arduino
2) Googling (research) indicate many ways to build a Walkie-Talkie communication device. But, Arduino seems to not be mentioned; likely because we have not identified the role if the Arduino! Oops. Let us assume for the moment that the Arduino will digitize an audio signal (analog) into a digital stream. Researching this with Google gives a few hits. One is:
Well... That did not look too good. While we can "control" and "display" the digitized audio, it does not seem from the write-ups that the audio is of high enough quality to be transmitted via RF to another Arduino to perform a DAC to recover the audio. Worst, the Arduino has no ADC hardware, so we would have to construct this ourselves.
2) more Googling... http://forum.arduino.cc/index.php?topic=51681.0
Ummm... This does not sound good. Grumpy_Mike has some excellent insight. Worst, no choice could be presented to suggest that we may actually be able to do this.
Continue to research and find someone that has digitized voice audio and been successful at recovering the audio in realtime with another Arduino. Or, rethink #1. If you were given 2 walkie talkies and 2 Arduinos, what could the Arduino provide to add-value to the project? Is the value added worth the investment? Now, you are thinking like an engineer!
My personal belief is it is "doable" but only with some assembler and some discrete components such as OpAmps and DAC chip on the receiving side.