Text Tracking FAQs | USPS

28777 (2USPS) with your tracking number as the content of the message. The text reply from USPS will be the latest tracking information for the item.
Send a text to 28777 (2USPS) with your tracking number and a keyword. Keywords tell USPS the specific information you want to know, such whether or not delivery has been attempted. See more on keywords under the heading “How do I use keywords?”
From the web site:

After tracking a package on the USPS Tracking® web site you may register to receive
— Read on www.usps.com/text-tracking/welcome.htm