I posted about Installing Frash on iPad and iPhone4
But the Frash package is still not stable enough (e.g. it messes up the default youtube plugin)
Somebody set up a repo with the Frash plugin and a SBSettings toggle so that you can toggle the effect of Frash.
To install Frash and the Frash toggle directly from cydia add this cydia source:
Previously I wrote about running Flash (codename: Frash) on iPad. Frash has now been ported to iPhone4. The installation procedure is same as that on iPad except you should use Frash-0.02.deb (mirror) – credits: Grant Pannell