Re this: I've long suspected that Guede actually did have a mobile phone in the period leading up to the murder (and during/shortly after the murder). I think it's difficult to imagine that a wide boy such as Guede, with his obvious links to the Perugia black market, and a seeming sideline in dealing, wouldn't have been able to get hold of a mobile phone. Indeed, I suspect he would have seen the possession of a mobile as a necessity - both for status reasons and for practical reasons.
I therefore suspect that Guede was savvy enough about mobile phone technology to believe that it would be possible for the police to trace his movements on the night of the murder. And if he'd made or received any calls or texts, then there is indeed a reasonable chance that his location could have been roughly tracked (assuming also that his mobile was not GSM-enabled, which it almost certainly was not).
So I think that Guede very probably threw away his mobile phone for that very reason, and obtained a new handset and SIM (or switched to another phone and SIM that he already had, but had not been using on the night of the murder). I suspect that the police didn't follow up on this properly. For example, had they obtained Egbaria's records, they could have figured out the number that Guede was using on 27th October, and tried to follow the SIM linked to that number on the night of the murder.