public static void askNumber(){
		System.out.println("Enter your phone number.");
		try {
			CustomerDetails.setNumber(keyboard.nextLine());
			if (CustomerDetails.number.length() < numberMin || CustomerDetails.number.length() > numberMax)
				throw new Exception();
			else
				checkExisting();
		} catch (Exception e) {
			System.out.println("INVALID: Number is too short or long (must be between " + numberMin + " and " + numberMax + " characters)");
			askNumber();
		}
	}