U-mobile was one of the first SIM-only options available in Japan. Using a part of the NTT Docomo network, they offer a fairly stable 4G connection all over Japan. However, the customer service options are not great as it's the company's policy to charge for a new SIM card if there's a fault with the one you already purchased.

Monthly Fee (Data only): From ¥2,570
Monthly Fee (Data + Calls + SMS): From ¥3,110
Cancellation Fee: ¥6,480 within 6 months
Free Cancellation: After 6 months

OCN is one of the largest home broadband providers in Japan and have recently branches out into providing mobile data SIM cards. They have competitive prices and regularly have campaigns to entice new customers to join.

Monthly Fee (Data only): From ¥972
Monthly Fee (Data + Calls + SMS): From ¥1,728
Cancellation Fee: ¥8,000
Free Cancellation: N/A

The internet shopping giant in Japan has also launched its take on SIM-only options as Rakuten Mobile. From very competitive prices to cheap phones, their online store offers discounts that are hard pressed to find elsewhere. A bonus for Rakuten customers is that you can use points earned through your SIM usage to pay for your phone bill or make purchases online.

Monthly Fee (Data only): From ¥972
Monthly Fee (Data + Calls + SMS): From ¥1,728
Cancellation Fee: ¥10,584 within 12 months
Free Cancellation: After 12 months

Mineo is a veteran in the area of providing SIM-only options. Originally started by using a part of the AU network, they now offer the option to choose between the AU and NTT Docomo networks. This means that if you have a locked phone on either of the networks, you are still able to sign up with Mineo for a cheaper contract.

Monthly Fee (Data only): From ¥972
Monthly Fee (Data + Calls + SMS): From ¥1,630
Cancellation Fee: ¥0

Freetel has definitely made a mark on the SIM-only market in Japan, using the NTT Docomo network to provide 4G service across Japan that's very stable. Not only does Freetel provide competitive prices for its contracts, it also has the option to pay for what data you use, meaning you could opt to pay less than the already low-cost fixed monthly fees in particular months, albeit with a bit of self-control. The company has also started to manufacture high-spec unlocked phones for low prices to go along with their contracts.

Monthly Fee (Data only): From ¥322
Monthly Fee (Data + Calls + SMS): From ¥1,078
Cancellation Fee: ¥0