Victoria, I'm still waiting to be let out of this 'ere box that you think I'm in.
Surely you don't want me to remain in ignorance ?
It's quite simple, really. If there is enough data available to establish a pattern of behaviour over the preceding period, then it will be possible to tell whether activity over the period in question (ie the abduction window) was anything out of the ordinary. If a picture can be built up over several days (ideally longer) of how or if these phones contacted each other, then that can be compared to contact that occurred during the abduction window.
Then, if it is believed that these phones were contacting each other during the abduction window in a way that wasn't consistent with a pre-established pattern, their pattern of contact post abduction window could also be looked at, including where the phones were in the following days. Even if the owners of the phones weren't known, knowing where they were at particular times, especially if there were three of them and they were in unusual locations, may be enough to start tracing the owners or users of the phones.
It's a painstaking, long-winded process, but potentially can lead to a breakthrough. The biggest difficulty though will be in getting the information from the various providers, let alone the analysis and generation of leads that then follows.