Mobile phone number formatting tool

Convert cell phone numbers to legible format, grouped 3 - 4 - 4; grouped 4 - 4 - 3

Among them, in the 3-4-4 grouping, the first 3 digits are the network identification number, the 4-7 digits are the area code, and the 8-11 digits are the subscriber number (randomly assigned, optional).

For example, 3-4-4:

13812345678 -> 138 1234 5678

For example, 4 - 4 - 3:

13812345678 -> 1381 2345 678