That's one tiny microphone! At about the size of a mature aphid, this wired Electret Microphone is perfect for your FONA.

This microphone's very similar to our PCB-mount Elecret Microphone but is significantly smaller and has pre-attached 65mm long wires.  We don't have a specific datasheet for it but it can be biased with 2V and 2K impedence. You do need an electret microphone amplifier to boost the millivolt-signal up to line level. The FONA has this amplifier part built into it but something like an Arduino does not.

We tested it with the FONA and it works great for voice purposes, you may also be able to use it with our other microphone amplifiers (like #1713 and #1063) and if you desolder the onboard microphones.