Many years ago it was done with junked Video
Tape Recorders and, from what I saw and read,
very successfully too.

If this is the same project that I remember, it's based mostly around
the TV tuner module from an old VCR.

The TV tuners work real nicely as they have a well-defined interface to
the VCO control voltage, mixer in, and mixer out. The VCO is also the
"right range" (VHF-Lo, VHF-Hi, UHF covers a lot of frequency!) at least
for 50MHz up to the top of the UHF TV band. I don't know what they did
for frequencies below 50MHz.

The TV tuner module is also nicely interface to (a handful of easily
soldered-to pins.)

Cellphones don't really have a well-defined module like the TV tuner in
them. They aren't broadband in the same way. Their synthesizers are
not broadband either.

Tim.