/** ******************************
 * United States mobile phone number *
 *********************************/
/**
 * Validates NANP (North American Numbering Plan) format
 * - Area code (NPA): 3 digits, first digit 2-9
 * - Exchange code (NXX): 3 digits, first digit 2-9
 * - Subscriber number: 4 digits
 *
 * reference: https://en.wikipedia.org/wiki/North_American_Numbering_Plan
 */
export declare function is_us_mobile_phone_prefix(tel: string): boolean;
/**
 * with/without +1 prefix
 */
export declare function is_us_mobile_phone(tel: number | string): boolean;
/**
 * very forgiving
 *
 * @returns +1xxxxxxxxxx if valid
 *          empty string if not valid
 *
 * US phone numbers follow NANP format:
 * - 10 digits total (after country code)
 * - Area code (NPA): 3 digits, first digit 2-9
 * - Exchange code (NXX): 3 digits, first digit 2-9
 * - Subscriber number: 4 digits
 *
 * reference: https://en.wikipedia.org/wiki/North_American_Numbering_Plan
 */
export declare function to_full_us_mobile_phone(tel: string | number): string;
/**
 * @returns +1 xxx xxx xxxx if valid
 */
export declare function format_us_mobile_phone(tel: string | number): string;