You can simulate vector flicker pretty easily, though it might irritate some people, so it should probably be an option. The iPhone -- even older generations -- should have ample power to do a pretty convincing X/Y monitor simulation, since vector graphic simulation itself isn't very demanding, so there should be plenty of cycles left over for flicker effects.
My own experiments have shown that GL based graphics can do vector flicker surprisingly well. The bigger issue I've struggled with is how to get the analog "look" right. Getting the "warm" feel of an analog signal is slightly more challenging than the phosphor decay. X/Y displays like the Quadrascan and Vectrex don't really have "pixels" per-se. Which means that aliasing is a no-no. (Something very prominent when drawing the thin lines of a vector display.)
I experimented with blurring, but that had a negative effect on the phosphor simulation. (Can you say "extreme smearing"?) The solution I landed on is to render sharp lines to a decaying backbuffer, then post-processes the image to give it an analog look. Throw a bit of sinusoidal disturbance into the post processing, and it should look just like the real thing!
BTW, I found the flicker to be surprisingly helpful in one respect. Vector displays were REALLY bright. So bright that it's near impossible to replicate on modern displays. The flicker has the effect of making it look brighter than it actually is. Which gives a better impression of the virtual display.
What do you get when you cross Robotron with Bomberman? - Coverfire HD