openBSC encryption

Hi, Till now I have always worked with simcards without knowing their ki so I was not using any encryption. I have recently bought some programmable simcards and gave them an IMSI and KI and tried to have them working with ‘encryption a5 1’ and ‘encryption a5 3’ and I faced some problems. First if I choose 'a5 3' the phone cannot connect to the BTS and nothing can be done, while if I set the encryption to 'a5 1’, the phone connects normally and can make and receive calls but sometimes the call fails for a reason that I don’t know. I have then tried the following setup: I have connected 3 phones A, B and C. A and B have no KI related to them so no encryption is applied while C was given a KI. If I call from A to B or from B to A, the call is done successfully every time, while if I call from either A or B to C or from C to A or B the call might work and might not. Is there something in the configuration that should be changed when adding the encryption support ? And how to enable the a5 3 encryption ? Best regards,