In the United States, the number of text messages sent per person per month has declined in recent years. According to the Pew Research Center, the average American adult sent 143 text messages per day in 2015, down from 164 messages per day in 2011. This decline is likely due to the rise of social media and the increasing popularity of messaging apps like WhatsApp, Facebook Messenger, and Snapchat, which allow users to send text messages, photos, and videos without having to pay for each individual message.

There are a number of factors that have contributed to the decline in text messaging in the United States:

1. The rise of social media: Social media platforms like Facebook and Twitter have become increasingly popular in recent years, and they have largely replaced text messaging as a way for people to communicate with each other. Social media platforms allow users to share photos, videos, and links, and they also make it easy for people to stay in touch with friends and family who live far away.

2. The increasing popularity of messaging apps: Messaging apps like WhatsApp, Facebook Messenger, and Snapchat have also contributed to the decline in text messaging. These apps allow users to send text messages, photos, and videos without having to pay for each individual message. They also offer a number of features that text messages do not, such as group chats, read receipts, and the ability to share live locations.

3. The unlimited texting plans: Many cell phone plans now include unlimited texting, which has made it less expensive for people to send text messages. This has contributed to the decline in text messaging, as people are less likely to worry about how many messages they send when they know they won't be charged for each one.

The decline in text messaging in the United States is likely to continue in the future, as social media and messaging apps become even more popular.