That's controlled by your service provider (Anveo in your case). You'd need to contact them.
Aside from that, it's a bad idea, and the service provider is unlikely to permit it. It would be tying up your OBi, ringing forever. If there was some sort of problem with the call, it would never give up.
Finally, why would you want to do that? I can't think of anyone nowadays who would put up with waiting longer than a minute for you to answer the phone, unless you are disabled, and your callers know it will take you several minutes to answer.