I'm unable to send SMS (text) messages from Galaxy smartphone (Hong-Kong version). How do I fix this?

I'm unable to send text messages to a specific contact, but can send messages to other contacts

If there is only one contact to which you're unable to send any text messages the problem very likely lies with the network and not with your device. Please contact your network operator to see if they know of a solution. If  possible it is also worth asking your contact to ask his or her network operator about the problem, too.

If the network operator(s) are unable to help, then please contact Samsung's customer support services for further assistance.

I'm unable to send text messages to any of my contacts

If you're unable to send any SMS (text) messages to any contacts, but your phone is otherwise perfectly functional, it suggests that your network operator's message center number stored in your device's settings is either missing or wrong. Follow these steps to check, and if necessary correct, that number.

If the text message still won't send, or if your phone already had the correct message center number stored, please follow the next steps to clear the data in the Messaging app.

Clear the Messaging app's data

Follow the steps below to perform a factory reset.