Hi Marcel,
 >
> is your private APN really an X25 network? We would normally expect types of IP, IPV6 or IPV4V6 and not plain X25. Are you asking for X25 network via AT+CGDCONT or does the network turn it into one?
>

The CGDCONT is quite clearly using an IP context type.  We don't even 
support X25 context type btw ;)

ofonod[1911]: Modem: > AT+CGDCONT=1,"IP","...."\r
ofonod[1911]: Modem: < \r\nOK\r\n
ofonod[1911]: drivers/atmodem/gprs-context.c:at_cgdcont_cb() ok 1
ofonod[1911]: Modem: > AT+CGDATA="PPP",1\r
ofonod[1911]: Modem: < \r\nCONNECT\r\n

Regards,
-Denis