Note Text reminders are an additional $5 a month plus 3 cents per text to your monthly subscription.
Summary
If you have text messaging set up in your account for Appointment Reminders, the response to your texts is in the Text Reminders report. You can use this report to find people who responded with something like Wrong Number.
Key Points
Go to Reports > Text Reminders
Search for words like Wrong in the Response column
When you get that reply it means the mobile phone number you have in the customer's account is not correct.
To find that type of response from your text messaging feature:
Go to Reports > Text Reminders
Filter the From date back to the beginning of the year or to when you started with Fieldwork.
Press CTRL + f (Windows) or Command (⌘) + f (Macintosh) and in the search box type "wrong" without the quotes.
You will see how many people responded with the word 'wrong' in the response column.
Sometimes they reply 'wrong number', other times the response is a little more colorful.
The customer name that the text was intended for is in the Customer column.
Click that customer's name to open the customer's billing page. Contact that person either by another phone number or their email address and ask for an updated mobile phone number.