Mary_H.... I think Dan O. addressed all this, including the fact that Massei also acknowledged that it is impossible to tell when or if phones are turned off or on with phone records.
On another matter - why anyone would ignore you is beyond me!
It's worth being technically accurate on this point:
Billing records tell you nothing except for actual traffic patterns to and from a given handset (strictly speaking, a given IMSI). However, network software is capable of telling whether a given handset (IMSI) is connected to network or not at any given time, and is also in theory capable of creating an archive of connection over time.
The crucial point is that it's impossible for any network to determine with certainty whether or not a lost connection is due to a) the handset having been turned off, or b) the handset being situated in a place with no signal coverage.
When a GSM mobile handset is switched on, it performs a handshake protocol with the network (assuming it is within network coverage) known as the IMSI attach protocol, which essentially involves the handset (IMSI) identifying itself to the network as available, and announcing its location (i.e. its connectivity to certain base stations). Once the handset is on, it sends periodic location updates to the network (i.e. "I'm still on, and I'm still where I was the last time you checked", or "I'm still on, but I've now moved to the area covered by a different base station".)
If the phone is switched off, it will send an IMSI detach message to the network (i.e. "I'm turning myself off now, don't bother looking for me if someone calls or texts me etc").
Both of the above events are logged and stored by the network, and are capable of being stored for longer periods (depending on the network's software systems). It is therefore potentially possible to look back and see the IMSI attach/detach records for a given handset on a certain day.
But...... if a handset falls out of network coverage, what will happen is this: the network will recognise that the handset has failed to communicate (either via a location update or with an IMSI detach), and the network will then perform an implicit IMSI detach (i.e. it will to all intents treat the handset as if it were switched off). If the handset then starts to receive signal coverage again (having been powered on all the while), it will immediately send a location update message to the network, which will then cancel the implicit IMSI detach and accept the handset back onto the network.
Now, the important thing is this: the network has no way whatsoever of being able to distinguish between the following two scenarios:
1. Handset switched on and talking to network
2. Handset remains switched on but falls out of signal coverage.
3. Handset remains switched on but now regains signal coverage.
and
1. Handset switched on and talking to network
2. Handset remains switched on but falls out of signal coverage.
3. Handset now switched off.
4. Handset switched back on, but still out of signal coverage.
5. Handset remains switched on but now regains signal coverage.
There can therefore be no certainty attached to the opinion that Sollecito manually switched off his handset that night, if it had fallen out of signal coverage in any case.