Do you have the original box to your phone? If someone you know has mysteriously gotten the same phone as you RIGHT when you lost it and you suspect they took it, go to a teacher (or supervisor, whoever is in charge of wherever it was taken) and ask them if you can see the back of the phone. If you take the battery out of the phone, there's a code in there. If you look at the IMEI code, and compare it to the IMEI code on the non-removable sticker on the box your phone came in, and it's the same code, then that phone IS yours.

No two IMEI codes are the same. It's like a serial number for your phone. If the original box you have in your possession matches the code on the phone - they took it. I know quite a few people who took their story to he principal when we were in school and would do that, and 9/10 times they got their phone back.

Don't just go out accusing people, but I figured I'd let you in on that tip.