How can I access hidden features on iPhone using manual dialling codes?

There are some global USSD (Unstructured Supplementary Service Data) codes that work across multiple mobile network operators and countries. Here are a few examples:

1. *#06#: This code is used to check the IMEI (International Mobile Equipment Identity) number of your phone. The IMEI is a unique identifier assigned to each mobile device, and it can be useful for tracking your phone if it's lost or stolen.
2. *#31#: This code is used to hide your phone number when making outgoing calls. If you enter this code followed by the phone number you want to call, your caller ID will be hidden from the recipient.
3. *#100#: This code is used to check your account balance on some mobile networks. If you enter this code and press the call button, you should receive a text message with your current balance.

However, it's important to note that not all USSD codes work across all mobile networks or in all countries. The specific codes and their functions may vary depending on your location and service provider. It's always a good idea to check with your mobile network operator to find out which USSD codes are available to you.