uBlox has released in January 2012 two new receivers with small form factor and carrier phase output: NEO-6P and NEO-6T.
Why not coupling with a Bluetooth transceiver (Roving Networks RN-4x) to give every mobile device the possibility of accessing high precision with -say- RTKLIB?
A logger functionality is always nice, so we added a smart Cortex-M3 MCU (STM32F102xB) and a micro SD card slot.
We are carrying out this project together with optimalsystem.de so feel free to contact them also.
The current version of the PCB has a switch connector for an internal active active antenna with u.FL connector and external active antenna with mMCX. Voltage is 3.3V.