Ok,
So putting two mics into the same intput doesnt work. I have left the mic on the phone, playing the tones down this mic works most of the time. I then soldered wires on to the back, and tied them onto the handset mic. Doing this stops the "internal" mic from picking up the tones, however the "external" mic still allows me to dial out.
My question is why is this the case? Why does the "internal" mic suddenly seem less sensitive when connecting up the "external" mic in parellel with it?
Looks like the Voltage divider or transformer is really the only way if I want to keep everything internal. I'll try a 600 ohm/600 ohm transformer, but is there a way of figuring out what I need or is it a suck it and see? Are there any disadvantages to using a voltage divider (resistors are easier to get), bearing in mind that sound quality isn't major as long as it sounds about right to the phone switch.
Thanks for your help guys and sorry for all the questions, I just like learning things and figuring out why things are bad and why things are good. And therefore, sorry for any stupid questions.