I read that by removing the GSM switch capability in a cellphone the voice calls would be more secure also if ciphering is enabled. My handset is a Sony Ericsson w610.
Here is the modification I included in the customize xml :
<enable-EPS-encryption-algorithm-128-EEA1>true</enable-EPS-encryption-algorithm-128-EEA1>
<enable-EPS-encryption-algorithm-128-EEA2>true</enable-EPS-encryption-algorithm-128-EEA2>
<enable-EPS-integrity-algorithm-128-EIA1>true</enable-EPS-integrity-algorithm-128-EIA1>
<enable-EPS-integrity-algorithm-128-EIA2>true</enable-EPS-integrity-algorithm-128-EIA2>
<remove-system-mode-option-gsm>true</remove-system-mode-option-gsm>
</network>
If there are any flaws in the lines, please feel free to suggest modifications.