Questions have been asked about the co incidence of the texts sent from GBC phone and Allison's phone connecting to the Internet at 6.31 am. A friend has explained to me that the way Apples iMessaging works is that IF both ends of the conversation have an iDevice (and in this case, they did - they were both iPhones) then that is detected as soon as the text message is sent, and the message goes via the Internet, and NOT via the telco 3G connection. Those iMessages are free, and show on the iPhone or iPad as a BLUE message from your end, as opposed to sending a text to somebody who does NOT have an iDevice (say an Android Samsung instead) in which case your messages show up in GREEN.
So when GBC sent his first text message at 06:31, it would have woken up Allisons phone - wherever it was - and logged it onto the Internet to receive the message. It would immediately be detected and identified as an iPhone. Once logged on, it would not have logged off again unless somebody actively did that by turning the phone off. And if the phone was in the one place, it would simply have remained logged on (including automatically checking for emails, texts, etc - pinging the towers Internet connection) until the battery ran out.
The big question is WHERE was Allisons phone when it got woken up by GBCs text message? It could have been in his pocket, or in the Captiva beside him with him chucking it out of the window or taking it out of the car somewhere that remained within reach of the FTP tower. And it should be pointed out that the FTP tower is right next to the overpass over the Centenary Highway, and reaches at least as far as the Kenmore Plaza, and probably further.