I haven't tried phonegap, though I've tried titanium, which worked but the performance made it ususable (I think it was on an ipod touch 3GS though, not sure about ipod touch 4).
There's also appmobi, which claims to have a canvas accelerator that boosts performance by 500%: appmobi.com
Hopefully with hardware acceleration coming soon to iOS HTML5, performance will be improved enough to make games for the platform!