You can retrieve data from the device with special equipment after opening the phone. This is beyond the typical "geek".

If you jailbreak the phone you can access all non protected data.

iOS Mail app uses DAPI correctly. For push mail when the phone is locked it will use a public key to encrypt the data.

I am unsure if even the Gmail app uses it correctly, I only tested the stock mail app.

If you have the an escrow key pair (ie. synced to iTunes) your are screwed. If should do a DFU mode restore to wipe the keybag completely.