Thank you for the answer. It works just fine and I've been at loss all this time and could only make calls and not answer incoming calls.
Below the screen, there are 3 groups of keys. On the left group of keys you should be able to see 3 keys aligned together, the key in the middle of them is the key used to answer calls. For more information regarding this, visit Sony Ericsson 905A page and download the manual.
Let me know how it goes.