I'm looking to use the FONA 808 with the TinyDuino with Li battery support, TinyShield Accelerometer, the TinyShield Protoboard, and potentially Mifare MFRC522 RFID Reader/Writer.

I'm relatively new to this stuff but I'm wanting to try and learn.  I'm a bit confused by this thread. The MFRC522 appears to require 3.3v.  I'm seeing where the TinyDuino no longer provides a 3.3v rail.  Would I basically need to wire the MFRC522 to the Protoboard and use a step-down to bring it from 5v to the necessary 3.3v?

From there, I should be good to go, correct?

You'll need a regulator plus level shifting for any output pins to the chip- if it's low speed SPI, that can be a resistor divider. Another option is finding a board with built in regulation and level shifting, like FONA and our accelerometer board have, which makes things a lot easier.

Sounds like an interesting project!