Finally I found the code to extend the ring time before answer. It seems by default Vodefone Blackberrys are set to only ring for 5 seconds before going into voice mail. Dialing the following sequence of characters and numbers extends this ring time to 15 seconds:
This will display the following message on your screen:
“Call Forwarding No Reply : All Teleservices forwarded to +0121your_mobile_num”
Press the “hang-up,” button to remove this message and your Blackberry should now to set to 15 seconds ring time before been forwarded to voicemail.
The ring time on the sequence of characters is the last number and must be a common denominator of 5 between between the range of 5 and 30 e.g. 20 for 20 seconds, 25 for 25 seconds, etc.