IIRC, when Melissa interviewed MR, she tweeted that she checked with LE, and the text came from Dylan's cell phone.
Yes, she said that. I don't find Melissa reliable. Moo
Elaine also seemed to confirm that on Dr Phil. The transcript for that portion of the show was posted a couple pages back, IIRC. I'll try to find it.
ETA: From
http://www.websleuths.com/forums/showthread.php?t=191821&page=4
Dr. Phil: I mean they live on these smart phones, and they text a lot.
ER: He did text… all the time.
Dr. Phil: Right, and at 9:30 that night, all texting stopped?
ER: Yes.
Dr. Phil: Is that unusual?
ER: Absolutely! Especially when he’s up there!
Dr. Phil: ‘Cos he’s a text animal. He…
ER: Yes.
Dr. Phil: That was his lifeline to the world. He…
ER: Exactly.
Dr. Phil: He was texting. So right up ‘till 9:30 he’s texting and then just zip… zero… So he could of gone to sleep, right?
ER: 9:30 seems a little early for Dylan, but…ummm
Dr. Phil: Okay, what time would he usually go to sleep?
ER: Probably about 11, midnight, somewhere around there
Dr. Phil: So 9:30 would be early.