if you suspect your phone is wiretapped, then cease all further communications from the device. sell said device, and purchase a new phone from ebay/craigslist that has a different IMEI. from there, you pickup a SIM from AT&T and load the sim with a 'reload' card purchased from any store (7eleven, cvs) with cash.

to communicate securely, i suggest you and the receiver use a client that supports OTR

better to be safe then sorry :)

EDIT: also if you must send via text message; i suggest you use a service like so: https://onetimesecret.com/ - the content of the link will be destroyed after a single view