With MVNOs and budget SIMs, signing up for a mobile line has gotten really easy these days. But here's a thing many people overlook: when you cancel your contract, you may be required to return the SIM card. SIM cards are technically rented from the carrier, so as a rule you have to send them back when you cancel. Whether or not return is required depends on the carrier, so make sure to check each company's official website.

Carrier-by-carrier comparison

  • mineo: return required for the D-plan only
  • UQ mobile: you can dispose of it yourself
  • Y!mobile: return required
  • DMM mobile: return required
  • OCN Mobile ONE: return required
  • Rakuten Mobile: return required
  • BIGLOBE Mobile: return required for Type D SIM cards only
  • LINE MOBILE: return required

※ For return addresses, please check each carrier's page.
※ The information above is taken from each company's official website.

How do I return my SIM card?

You need to send the SIM card by post to the address designated by your carrier. As a rule, the sender (you) covers the postage. For details on how to return it, check the page of the carrier you contracted with.

What's the cheapest way to return a SIM card?

You probably want to keep postage as low as possible. The method I'd recommend is using a "mini letter" (ミニレター). Here's what an actual mini letter looks like.

A mini letter (postal stationery sold at Japan Post counters)

When you fold it up, it turns into a tiny envelope.

The mini letter folded into envelope form

It's the perfect size for tucking a SIM card inside.

A SIM card placed inside the mini letter

A mini letter can carry up to 25g, and the postage is 62 yen — the same as a postcard. You can buy them at any post office counter, and to send one all you have to do is drop it in a postbox, so it's super easy.

The completed mini letter ready to be mailed

Can you send it on a postcard?

For what it's worth, it looks like you could send a SIM card on a postcard as well, as long as it's firmly stuck on. But the SIM card will be exposed, so if it peels off mid-transit, you've got a problem. You also need to keep the total weight under 6g.

Q. Can I attach paper to the front of a postcard and send it?
A. As long as it is paper, a sticker, a photograph, or similar thin material, and it is fully adhered so that it cannot easily peel off, it can be sent.

https://www.post.japanpost.jp/question/44.html