*** 11/27/2016 Update:
My plan to use a second cell phone with a data plan failed spectacularly in Japan. A traveling companion had another phone for which we attempted to get a SIM card in Japan. That also failed. So I was unable to do any of the GPS mapping in Japan I hoped to do.
Here’s a new blog entry explaining what went wrong.
When traveling abroad, you may or may not be able to use your existing cell phone. There are several possibilities:
I. You can use your phone
II. You can use your phone, but will use a different SIM card while abroad*
III. You cannot use your phone; you will need to rent, borrow, or use another phone while traveling.
I. Using your own phone
The simplest way to find out whether you can use your own phone is to call and ask your carrier. They can look up the specifications on your phone and review your current plan to see if it will work. Depending on your phone and your needs, you may opt for:
a. a plan with voice minutes and texting, and limited data
b. a plan with data, but no voice or text
c. a plan with all of the above
Your phone and your carrier may have limited options, so ask specific questions. If you phone will work above, there may need to be some settings changes made to the phone. Your carrier can instruct you on how to do this, which you will need whether you decide to use your carrier or a different when you travel. You will want to ask a bunch of questions to decide whether to use your regular carrier abroad. For this example, we will assume you are traveling to Japan:
1. Are phone calls you make in Japan to Japanese numbers charged the same as calls you make in Japan to the US?
2. Are phone calls you receive in Japan from Japanese callers charged the same as calls you receive in Japan from calls originated in the US?
3. What is the charge per text to Japanese numbers vs. US numbers?
4. What is the charge for texts received from Japanese vs. US numbers? Some plans charge less for incoming texts (sometimes even free) and more for outgoing texts.
5. How much data do you get? How much do you get charged if you go over? Does it charge automatically, or do you get a warning first?
They may also have a pay-as-you go option, but depending on your voice, text, and data needs, that can get very pricey, so caveat emptor!
Once you have reviewed all your options with your existing phone and existing carrier, compare them against other possible carriers.
II. Using your phone with a different SIM card
You can search the internet or call other carriers to see what international plans they offer. You will want to ask all the questions above. If you find a plan that will fit your needs and your budget, you will buy a new sim card, which you will swap out with your existing sim card. Save your original sim card in a safe place! You will need it when you get home.*
III. Using A Different Phone
If you have another phone that will work abroad, you can simply purchase a SIM card (see II above) and use it during your trip. If you take your existing phone with you, be sure to turn it off and put it in airplane mode to prevent you from receiving unexpected (and costly) phone calls or text messages, or racking up costly data use fees!
IV. Additional Considerations
If you have a decent data plan or can find decent WIFI signals, you can make internet phone calls using any of a number of internet phone applications. Of course, both parties will have to be online for it to work, so you will either need to schedule ahead of time, or if you have free/cheap texting, you can send a quick text to let the other person know you are available. If you and your family and friends all use the same platform (e.g. Android), there are many apps. If you have some who use Android and some who use iPhone, you will need a cross-platform application (e.g. Skype, Google voice, etc.).
Auto Text Responder
If you are not going to take your phone with you, you can investigate setting up an autoresponder for incoming text messages. Just like email auto-reply setups, some phone apps allow you to set an autoresponse for incoming text messages. A couple of caveats:
1. Your phone will need to be on to respond. Therefore, you’ll need to leave it plugged in so it doesn’t die during your trip.
2. Text charges will apply. If you have unlimited texting, no problem.
If you take your phone with you on your trip, be very careful about using an auto-responder. Since texting can be very expensive abroad (depending on your plan), you could rack up serious fees if your your phone is on and autoresponding while you are abroad. One pay-as-you-go plan I found cost $.50 for outgoing texts and $.05 for incoming texts. So you would be paying 55 cents for every text your phone auto-replied to during your trip!
How to place and receive phones?
If you are making calls in Japan, research ahead of time how to make domestic (from Japan to Japan) calls, as well as international (from Japan to US) calls. Also, research how your family and friends may call you (US to Japan), assuming you want to receive calls while you are traveling.
Japan’s country code is 81, so to call Japan from the US, dial:
011-81-<city/area code>-<local number (usually 9 digits)>
Calling a Japanese cell phone from the US, you will just use a 70, 80, or 90 as the city/area code.
To call the US from Japan, dial:
010-1-(area code)-(local number)
Here is an excellent web page with international dialing instructions (including the current local time).
As I wrote elsewhere, your phone charger will likely work just fine in Japan. However, if your phone uses a unique connector (e.g. is not a standard microUSB or iPhone lightning cable), you may want to bring a backup. It’d be a shame if you lost your cable, or it broke and you couldn’t charge your phone. Extra cables and chargers can be easily found on the cheap on Ebay.