/** ******************************
 * Vietnam mobile phone number *
 *********************************/
/**
 * Checks if the number starts with a valid Vietnam mobile phone prefix
 *
 * Valid prefixes: 09x, 08x, 07x, 03x, or 05x (where x is any digit)
 * Format: 09/08/07/05/03xx xxx xxx (10 digits with leading 0 in local format)
 * Reference: https://en.wikipedia.org/wiki/Telephone_numbers_in_Vietnam
 */
export declare function is_vn_mobile_phone_prefix(tel: string): boolean;
/**
 * with/without +84 prefix
 */
export declare function is_vn_mobile_phone(tel: number | string): boolean;
/**
 * very forgiving
 *
 * @returns +84xxxxxxxxx if valid (9 digits after country code, NO leading 0 in internal format)
 *          empty string if not valid
 *
 * Format notes:
 * - Local format: 091 234 5678 (10 digits WITH leading 0) - used in Vietnam
 * - Internal format: +84 98 765 4321 (9 digits after +84, NO leading 0) - always 9 digits
 * - Display format: +84 98 765 4321 (formatted by format_vn_mobile_phone)
 */
export declare function to_full_vn_mobile_phone(tel: string | number): string;
/**
 * @returns +84 AA BBB BBBB if valid
 */
export declare function format_vn_mobile_phone(tel: string | number): string;