Would a cell phone or and ipod charge off a 550?
Under certain conditions, yes. But, again I have to ask what the additional electrical drain magnitude is. What are the power requirements of your cell phone and iPod?
Realize that the 550 alternator makes electrical power only when spinning and at a rate variable with the RPM.
With the headlight low beam on, the bike's steady state drain is about 10 amps or 128 watts.
The alternator output at idle is only about 50 watts, which means the battery is supplying sustaining power.
The alternator makes enough power at 2000 RPM to begin putting energy back into the battery that was taken out during idle.
The battery recharge gets much better at higher RPMs with 150 watt production.
Any additional electrical load placed on the bike will increase battery depletion below the alternator output/bike load break point RPM, and delay battery charge restoration above that RPM.
This may be NO issue if your common riding regime makes the engine spin above 3000 RPM most of the time. It is the time spent below the RPM breakpoint that depletes and taxes the battery. When the battery depletes enough, the coils stop firing the spark plugs. Both the cell phone and iPod will be quite handy at that time.
My cell phone charges with 3.7 Watts. I wouldn't worry about that additional load, unless I was in stop and go traffic and idling most of the time. Even then, I would turn off the headlight's 40 watt drain before worrying about the cell phone draw. I don't know what an iPod charges at. Wouldn't expect much, though. It's likely marked on it's charger somewhere.
Cheers,