So I have a Sprint CDMA 4S and plan on giving the phone to my parents in Sept./Oct. when they travel abroad to Asia on vacation for about 2-3 months. (I hope the new iPhone will come out by then, so I can just add it to my plan, not leaving me without a phone.) Because I'm afraid they might inadvertently change the settings on the 4S and I'd be hit with these roaming international charges, I advised them to leave the Sim Card Home here with me in the States and purchase a local sim card to call locally/internationally. So my questions are (this being my and now their first iPhone): 1. Would there be a disadvantage to leaving the sim card here at home? 2. Are they able to still text message by way of wi-fi & iMessage without the "original sim card" in the slot and not be hit with local/international text charges? Also, when I have my 4S in my pocket it will at times call the last number I dialed without me knowing it. This has happened to other friends of mine that have an iPhone - wouldn't want this to happen to my parents if they left the "original sim card" in the iphone and later dialed my number without them knowing it dialed while abroad. As you can read, I'm covering all possible scenarios. THANKS !!!