Pax Vobiscum,
I believe that inbound calls will be allowed, and at $2-00 per minute, it would be equivalent to the top end international roaming costs, though I'm sure market forces will have an effect.
On the point regarding congestion / cell failure, all these possibilities were tested and the mobile phones did not present any problems at any time. If the picocell failed, a digital mobile phone is too distant from any ground cell to log on and the metal body of the plane would severely attenuate any signal. Most ground antennae do not radiate much above horizontal.