We strongly recommend everyone to get a UK giffgaff SIM card for receiving verification codes.

giffgaff is a new low-cost carrier from the UK, owned by one of the UK's three major carriers, O2. Founded in 2009, it features no physical stores, fully online customer service, and flexible plans to reduce user costs, making it especially suitable for short-term tourists and UK students.

It supports global roaming, allowing sending and receiving texts, making calls, and internet access in China. The main advantage is that it’s really cheap—top up £10 and get £5 free, which is perfect for receiving verification codes domestically.

How to get it
Previously, you could apply for free on the official website, but due to excessive exploitation, the application channels for mainland China and Hong Kong/Macau have been closed. You can buy an inactive SIM card on the exchange to activate it.

giffgaff Number Retention Strategy
Overseas carriers generally require number retention, and gg cards require a change in the balance every 180 days; otherwise, the number will be frozen. The simplest way to keep the number in China is to send a text message, which can be sent to both domestic and international numbers. Each message costs £0.3, so annual costs are about £0.6, less than 6 RMB. After each recharge or usage, the number retention period resets from the date of the balance change. The first recharge also counts as a balance change, so as long as the number is kept active within 180 days, it should be fine. In theory, the £15 balance on the card can last over 20 years.