None. There is no evidence that any US mobile carrier places more value in protecting the security and privacy of your data than their profits. They will not sign HIPAA BAA agreements, they do not follow US-CERT or NIST security protocols, and have repeatedly been found to market your information.
Allow NOTHING of value to be seen by them. Use VPN to transmit data. Use encrypted communications for your voice and text messages.
Be responsible for your information, because they won’t be.