I will be entirely honest with you: every time I need to look up the PadFone to make sure I am not getting it confused with the FonePad.
An older model but it gets the point across.
The upcoming PadFone Mini is expected to be a phone of some size (probably smaller than the 5" Pad Fone Infinity) with a dock of some other unknown size. The phone was briefly mentioned in a China Times article back in September. There it was expected to have a 4-inch display on the handset and a 7-inch display on the tablet dock. According to Engadget's interpretation of the VR-Zone leak (who saw that coming?) that might have changed since then.
The device itself is expected to be based on the quad-core Qualcomm Snapdragon 400 SoC, run Android 4.3 (Jelly Bean), and have a handset resolution of 960×540. That is about all that we have even the slightest clue about at this point.
No word yet on whether this device will even be available in North America though. For that, we will probably need to wait until the actual announcement (or even later).