A10Thunderbolt

should be simple: I ve had no problem doing this on other phones but
(it's DAY #2 with the XPERIA, added 4.0 ICS last night)

How do I BLOCK CALLS by incoming number ?
..lowlife COLLECTION AGENCIES (2) are already looking for the LAST holder of this phone number..

Jake-SonyXperia

You can not block numbers using the handsets software, you would need to download software from the Play Store to perform such a task.