Unreliable message delivery via @txt.att.net

I work closely with the facilities/maintenance team of a hospital and they receive HVAC notification messages of failures or problems with the system or its components via email and text. These messages are sent out simultaneously from the HVAC management system to an email address and a cell phone number using @txt.att.net. While the email message transmissions have remained consistent for at least a decade, in the past year the text messages have been sporadic at best. A solution for this problem is highly important to us as we have staff who rely on their text message notifications to be alerted to after-hours problems.