I've decided to implement GPIO IRQ for the handset switch pin, reset pin, and keypad active pin. Using the GPIO ISR to switch states makes everything a bit easier.

I measured the reset/handset switch and mapped how it works. It has 8 pins and you can use some of the pins differently depending on the type of switching action you want. From what I could tell only 6 pins are used.
For the handset, use the pins that close the switch when the handset is off.
For the reset, use the pins that close the switch from reset to handset on.

I've disconnected the toggle switch and connected the handset switch instead. I've disconnected the push button and connected the R button. I will use the push button to simulate a URC from the modem later.

I checked all the connections and powered the breadboard up. There is humming on the DTMF audio output, I have no decoupling capacitors or LDO. Putting my finger on the MCP6002 increases the humming. :)

I'm working on making the interrupts work but just when you get into 'the zone', time's up...