If you can swap that iPhone 4 for an iPad2 (with some change, even), then that may give you the best bang for the buck.

Meaning, it's a low maintenance device that your mom and bro can operate and enjoy on their own and make use to communicate with you too (video chat, etc). Oh, and it's currently a pretty dang hot item too... so I'm guessing that getting an iPad2 from you will really excite them.

On top of that, you're giving them something magical (i kid... i kid...).