We don't know what we don't know until we ask questions of ourselves and our environment. Here is Ray's take on the technical issues of cellular or hand phones:
Interesting how important mobile phones have become to all of us. Without them we feel like we are cut off from our friends and the companies we do business with. Traveling overseas can be a real problem when trying to keep in touch.
Pat and I had service with AT&T for many years. I didn't want to change carriers, primarily because I had been with them long enough that my data portion remained unlimited, having been grandfathered in. I have talked to several people that remain with AT&T because of their grandfathered, unlimited data plans. Guess what! We changed and don't regret it at all.
While we were in Charlotte, planning our move to Singapore, Tom told me about talking to T-Mobile and that I should go see them. I did. I cancelled our AT&T service and paid the penalties for early termination and paid off the phones. I took our existing phone numbers with us to T-Mobile and that change happened before I left the T-Mobile store. Oh, and our total bill went down!
We now have no roaming charges when we travel the world, including unlimited data. If we are somewhere with wifi, calls and texts to, and from the U.S. are free! Otherwise, the cost is $0.20/minute. That is also the cost of calls to/from non-U.S. numbers. One of the best advantages is that my data applications I rely on work every where with no additional costs. I don't have to turn off my email, texting and other apps, just because I am not in the U.S..
The primary disadvantage is not have a local number when staying in another country. That means that local business and new friends are not likely to call you because they probably don't have international calling with their plans. There are two options to solve this problem: (1) Buy an unlocked phone with dual-SIM capability (I just got confirmation from T-Mobile that they don't sell such a phone, but you can use one with their system); or, (2) getting a cheap, unlocked, non-smart phone for use with a local SIM card. It is most important that the phone is unlocked, meaning it can use SIM cards from all the different places you want to visit.
Here in Singapore, Pat and I both use our T-Mobile phones for contacting friends in the U.S.. However, Pat also has a phone and service from a local mobile carrier.
Here is an excerpt from an email I sent to a couple of people regarding mobile phones and travel:
I mentioned Pat and I had T-Mobile cell phones and let you know some of the advantages I consider worthwhile. We switched from ATT and actually paid the penalty to leave them, as I knew we would be out of the country for a long time and needed a more global solution. When I saw the benefits that a T-Mobile account offered, I knew that was what I wanted.
Here is a part of their website that is relevant (this is the plan we are on):
We pay $80/month for 2 lines (we have paid off our phones, so there is no amount included for a subsidized phone. That $80 covers unlimited data (including in Singapore and lots of other countries), unlimited calling back to the U.S. if connected to WiFi (likewise for incoming calls from the U.S.), and almost all other calls are at $0.20/minute. That is quite a bit cheaper than anything ATT offers. Our ATT bill was nearly $140/month and I was grandfathered in on their unlimited data plan. And it was certainly worth leaving them!
I think your current iPhone may be unlocked, but you need to check with ATT. If you have paid off your phone and are no longer being subsidized, they may unlock it, if it isn't already. I just don't remember having to do anything with Pat's iPhone to unlock it. I did have to have an unlock code for my Galaxy S4, which they gave me a couple of days after I cleared my bill.