T46S using VPN with AES-256-CBC Ciphers and SHA256

[Venkymms]

We have several T46s handsets using openvpn very successfully. We need to use a higher encryption ie AES-256-CBC and SHA256. Tried updating the an existing vpn handset and I can't get it to work (phone not registering). Is this possible on the T46s handset ? How do I get it to work.