If you're an emancipated minor who buys your own phones and pays your own bills, you can stop the school from taking it.
Otherwise there's absolutely nothing you can do.
@ Wendy:
Sec. 37.082. POSSESSION OF PAGING DEVICES. (a) The board of trustees of a school district may adopt a policy prohibiting a student from possessing a paging device while on school property or while attending a school-sponsored or school-related activity on or off school property. The policy may establish disciplinary measures to be imposed for violation of the prohibition and may provide for confiscation of the paging device.
(b) The policy may provide for the district to:
(1) dispose of a confiscated paging device in any reasonable manner after having provided the student's parent and the company whose name and address or telephone number appear on the device 30 days' prior notice of its intent to dispose of that device. The notice shall include the serial number of the device and may be made by telephone, telegraph, or in writing; and
(2) charge the owner of the device or the student's parent an administrative fee not to exceed $15 before it releases the device.
(c) In this section, "paging device" means a telecommunications device that emits an audible signal, vibrates, displays a message, or otherwise summons or delivers a communication to the possessor. The term does not include an amateur radio under the control of an operator who holds an amateur radio station license issued by the Federal Communications Commission.
Case law provides that an emancipated minor has no parent from which the school can notify of disposal. Further, depriving an emancipated minor of their phone effectively cuts them off from emergency services and poses a danger to health and safety.
You are wrong on this one.