How I read it is that Corrie's phone came within range of the BM mast at 4.58am and remained there until 8am.
Now as I understand it (and I could be wrong) phones ping a mast when they come within its range, a sort of "Hello!", and ping when they leave to say "Farewell!".
If the phone is completely silent, ie no calls, text messages, emails or any other activity going on, they will not ping again until they need to, eg to confirm their whereabouts for some sort of communication. A call comes in. A tweet goes out. An app updates.
IF there is no activity to cause a ping, the phone would only be in contact with the mast to say Farewell. From the info we have, it appears the Corrie's phone did NOT sign off from the BM mast so was still in its area when it died at around 8am.
So if the police have evidence of activity on the phone up to 8am that's almost certainly because it was active in some way. That doesn't have to be deliberately made communication such as a call or tweet, it could simply be that an email comes in or suchlike.
Quite a few weeks ago the Police were asking for sightings of Corrie in the BM area up to 8am, so to me that means they thought it very possible that he was with his phone until it died.