I recently had a case where I sent a subpoena to AT&T for records associated with a mobility IP address. The IP in question was used to create a fake Instagram account on which possible CP was posted. AT&T's response was "the requested wireless IP assignment records are not created or maintained in the normal course of business and AT&T is unable to isolate or identify any individual account or device". I called AT&T's compliance center and the rep I talked to confirmed they did not keep logs of mobile/wireless IP address usage. Has anyone else had this issue?  

I'd say that's accurate. Much leg work here, but get the IP log from Instagram. Maybe one of them links back to the suspects home wi-fi? Maybe Instagram can provide you with an IMEI/MEID linked to the account?
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Ed

I'm not a cellular technology expert, but I did stay at a Holiday Inn Express last night. 

Thanks for the response. I got the IP log as well, unfortunately the account was only accessed at the time it was created for a period of a few minutes, and the only IP was the one I mentioned. My only other option is to get the records for the email address (which was likely created shortly before the Instagram account), and hope a different IP was used.