What is a text msg from unknown address that just says mms

[AC Question]

Why did i receive a text from unknown address that says mms it looks like a regular txt but all it says is mms and nothing else shows

 

[Mr Mendelli]

How long have you had your device? Way back on my first mobile phone, Verizon said a test message would be sent to test my service roughly twenty-four hours after it's activation.