If the first and second digits of the call you receive are 0, that is, 00, it is usually an international call from outside China. See: International call.
You can query the area code by entering more numbers after the first and second numbers 00, for example:
00 1: USA
0086: China
00852: Hong Kong
The third and fourth digits after the first and second digits 00 can be:
000:0000、000 1、0002、0003、0004、0005、0006、0007、0008、0009
00 1:00 10、00 1 1、00 12、00 13、00 14、00 15、00 16、00 17、00 18、00 19
002:0020、002 1、0022、0023、0024、0025、0026、0027、0028、0029
003:0030、003 1、0032、0033、0034、0035、0036、0037、0038、0039
004:0040、004 1、0042、0043、0044、0045、0046、0047、0048、0049
005:0050、005 1、0052、0053、0054、0055、0056、0057、0058、0059
006:0060、006 1、0062、0063、0064、0065、0066、0067、0068、0069
007:0070、007 1、0072、0073、0074、0075、0076、0077、0078、0079
008:0080、008 1、0082、0083、0084、0085、0086、0087、0088、0089
009:0090、009 1、0092、0093、0094、0095、0096、0097、0098、0099
See: 00,01,02,03,04,05,06,07,08,09.
Safety tip: Due to telephone fraud, SMS trap, luring to call back international calls, luring to call back toll stations and other traps, please answer and call back carefully when encountering strange calls. If you use a toll-free phone/mobile phone, you can answer it at will and ask the source of the other party's phone. If you need to call back, you'd better use a public phone without knowing the details of the other party. Don't believe in winning prizes, impersonating acquaintances, impersonating banks, etc. Don't remit money or transfer money to strangers before you fully identify yourself, and don't disclose your bank account number and password.