I found something interesting on the internet today, while browsing for rtl_sdr related information. It seems like a guy called steve-m has fed his rtl_sdr dongle a clock from his mobile phone. Here is a picture:
http://steve-m.de/pictures/rtlsdr_external_clock.jpg
Now mobile phone networks can be used to estimate the frequency error of your oscillator, because base stations will have clocks that are in sync to a global reference. I think this is what steve-m is aiming for. Has anyone else attempted to do this? I'd be interested to hear about your experiences.
It would be neat if a $8 dongle and a $20 cell phone could be combined to create a SDR locked to a global reference.
juha