After Conan saw a message coming from his cell phone, he ordered Detective Boys to go back to their room, the message could be about BO had been in the train or Sherry. Who is the one sending message to Conan? First, we can confirm it's not Sera.
Amuro: Conan considered Amuro as pain-in-the-neck, no way Conan gave Amuro his phone number. Amuro said just leave Kogoro to solve a case, his real meaning could be that he going to secretly plan something while Conan and Kogoro is not around.
Okiya: Conan's most trusted person, it won't be surprise that he had Conan's phone number. Furthermore, we can delete him from be the suspect as Bourbon. No way Okiya is Yusaku in disguise, otherwise what is the reason Okiya thinks"I see...so that's how it is..." when he saw Conan using Shinichi's name to make a phone call in File 813.
Scar Akai: Conan is shocked when he heard there is Akai with a scar, so no way to be him. When letting Jodie, Camel, Okiya and Sera (in File 801) to see him, he wearing a same cap. However in this series, why changing a cap and scar is bigger than usual, it's obviously disguised by second person. Even though Sera, Okiya, Amuro and Scar Akai version 2.0 were appeared at a same time, the possibility of Amuro being the original Scar Akai is still available.
Vermouth: If Vermouth sending message to Conan, the detail could be about BO found Sherry or issue a challenge to Conan. If that mystery woman with Okiya is Vermouth is too straight forward, but that woman is identical to the same way Vermouth disguised back to Vol 54 File 1(Ep 464-465), but will Gosho create a same disguise as same person.
http://www.dctp.ws/V54-Reader/V54-1Read/A4.html
http://imgsrc.baidu.com/forum/pic/item/ ... ef6dda.jpg
http://tieba.baidu.com/p/1628650505
FBI: Jodie is the only one FBI agent made a phone call to Conan, but FBI still no-show in Series Part 3, since Okiya and Amuro appeared too, wish that FBI appeared next. FBI had no interest to ride a mystery train unless they investigated there is BO members inside a train and informed Conan about that. By the way, it is too odd for BO confrontation series without FBI involved.
Yusaku or Yukiko: The favourite choice for all the fans, but the problem is how do they know there is BO members in a train, Vermouth is the only BO member that Yukiko ever meet. Most people said that mystery woman is Yukiko, like almost everybody guessed the mystery woman during London Case is Yukiko and the answer is correct. Then what is the relationship between Okiya and Yukiko?
Finally, how do Conan solve a case, Conan may need Kogoro to fall asleep in order not to interrupt Conan's deduction, but if using tranquilizer dart to put Kogoro to sleep, Sera may discover the secret of Sleeping Kogoro, then Conan still need to pretend to call Shinichi on phone and solve a case.