On Friday, two SIM card vending machines were launched at Narita International Airport aimed at making travel easier for Japan's increasing number of inbound tourists.

After featuring a story on the new machines in The Japan Times, feedback indicated that readers wanted to know more.

So, in the interests of seeing how it all works, I went off to buy a SIM card for my Zenfone 5 SIM-free smartphone.

Instead of Narita, I took a short trip to Aqua City in the Tokyo's Odaiba district, where operator NTT Communications Inc. has the same vending machine.

The SIM card dispenser is found on the third floor. On the left of the machine is a display window with SIM cards, phones and other products for sale, while on the right is a touchscreen display to make your purchase.

The machine offers two types of prepaid SIM cards: One priced at ¥5,346 for 14 days and the other at ¥3,726 for seven days, both including sales tax.

Smartphones, mobile routers and accessories are also available at the vending machines, but smartphones and routers can only be purchased when you buy one of the SIM cards. That means, no SIM, no sale of a smartphone or router.

For this exercise, I chose the seven-day plan.

Next, you are prompted to select the SIM card size. I actually forgot what size SIM fits into my Zenfone 5, so I had to Google that with a separate smartphone I luckily had with me . . .

If this was the airport and you've just arrived in Japan, chances are as a tourist you do not have Internet connection to check your SIM card size, like I did. My advice: Check this before you travel, write it down on a piece of paper and keep it handy in case you need it.

Next step is paying for the purchase with a credit card. The vending machines accept Visa, MasterCard, JCB, American Express and Diners Club. You can't pay by cash.

The purchase is done!

NTT Communications use NTT Docomo's network for its service, so the SIM cards are supplied by Docomo. The service is offered at a maximum download speed of 150 megabits per second and 50 Mbps for the upload speed. If the amount of transmitted data exceeds 100 MB a day, the network speed will slow down.

One important caveat is that this is a data communication-only SIM, meaning you can't make voice calls. But this may not be a problem if you are a user of Internet phone services such as Line and Skype.

But you're not finished yet. Now, you need to activate the SIM card, which can be done at the vending machine.

The first step is to scan the bar code printed on the SIM card.

Then, you need to scan your passport on the scanner built into the vending machine.

After that, you need to type in your email address and contact number in Japan, which can be your hotel's phone number.

That's it. The entire process to activate the SIM card takes about 5 to 6 minutes. But I was doing it while taking pictures, too, so the process could be shorter.

My impression is that it should be fairly easy for everyone, though the SIM card size may confuse some people. Again, it's a good idea to check your SIM card size before you depart for Japan.

And if you're wondering what smartphones or tablets are compatible with the SIMs offered by NTT Communications, here's a list.

Now, it's time to check if the SIM really works.

I inserted the SIM into my Zenfone 5, which is an Android device, and then went to the "Mobile networks" setting and then "Access Point Names."

I then chose "OCN mobile One," which is the name of the mobile connection service operated by NTT Communications.

I have done this setup before, so it was quite easy for me to get the SIM connected to the network, but if you have never done this before, it might be confusing. In that case, you might want to ask someone who is familiar with this kind of procedure.

Voila, it's working!