If you want to prevent that number from being able to call your Sony Ericsson ST17i-BKW, you can add a number to your ‘Reject List’.
To add a number to the Reject List , you just need to follow the instructions:
Go to your Sony Ericsson ST17i-BKW
Open the contact page
Select number from the list
Press Menu key
Add to reject list.
Please note that in your Sony Ericsson ST17i-BKW, the Reject List just can block calls from the blocked numbers which are shown with the common blue No symbol
You also can use Third-party apps for blocking phone calls in the Sony Ericsson ST17i-BKW.
This application both blocks calls and SMS which are unwanted, and can help manage a blacklist. It is so easy and lightweight, and does not consume any of your device’s battery power.