Use app called Call Blocker to block incoming calls from a number.
- Help you to ban/block calls from specific contacts.
- white list or Black list specific numbers
Check this user guide for Ginger Bread to know about Android User Interfaces(While search for User Interfaces Google will give details about Programming UI in android applications)..
Or if you don't want to use 3rd party apps
Black List Feature
The Black list feature allows you to choose phone numbers that you don’t want to receive calls from and block them. When the black listed phone numbers tries to reach you, they will always get a busy tone.
Here’s how you can block calls on Android.
Follow these steps to blacklist phone numbers:
1.From the home screen, tap ‘Menu’.
3.Then select ‘Call Settings’ to reach ‘Black List’.
4.Tap on ‘Black List’ option to ‘Add Phone Number’. Type the phone number manually or insert from the contact list.
5.Click ‘ok’ and you are done.
6.You can also blacklist the phone number by selecting the contact and tapping the menu of the contact to select ‘Add to Black List’. Or else, when the number that you want to block calls you, follow the same method. You can easily remove the blocked numbers from the blacklist by going back to the list and unchecking the contact.
NOTE: This depends on ROM you are using.