It's for ppl that have Samsung Galaxy phones and or are with the same company u have.. it let's u text n reply n both u can see when the other is writing or seen the text. And it helps send pix and video to each other quicker. But it's really just letn u no they have Samsung Galaxy phones
The galaxy S10 and the Samsung messages app are RCS compatible or capable. Your carrier is also running a RCS network infrastructure.
The messages app scans your contacts and connects to your your carrier database and determines how many of your contacts are using RCS capable phones and their RCS network infrastructure. It marks the contacts with a blue dot if they have met the requirements for sending and receiving messages in chat mode.
You should be able to send and receive multiple large image files at full resolution. Also uncompressed video files and your text messages character count limit should go much higher. When you send mms and text messages to contacts without the blue marker the messages app will send and receive mms and text messages using the standard messaging format.
It's not the same carrier as in ATT OR Verizon, it's the same brand and type of phone on my messages. It only shows the blue for on the S10+ on mine. My son has a Samsung as well as Multiple others in my family, it only shows the blue for on the people with the same S10+ as me.
It's actually "Advanced messaging"
So whoever's has that enabled on their samsung/Att phone. It will show u. I tested it out with a few of my family members and sure enough it was it. When I turned it off the blue dot went away and when I turned it on. I can see all the blue dots and they can see mine.
It is for which contacts you can make VIDEO CALLS to through the STANDARD CALLING APP. I have 7 phones on my plan, 3 are S9 plus 2 are note 10 plus. 4 of us have the blue dot and can video chat, my daughter has a note 10 plus UNLOCKED VERSION hers does not have the blue dot and we CANT VIDEO CHAT THROUGH THE STANDARD CALLING APP .... we can only video chat through messenger. Because of that I am trading her phone in for the S20 carrier version. I didnt know that the unlocked versions didnt offer video calling, that software comes from the carriers and they cant add it for you and I dont want to add it myself. SO TO ANSWER YOUR QUESTION, THE BLUE DOT MEANS YOU CAN VIDEO CHAT WITH YOUR CONTACT REGARDLESS IF YOU ARE AT&T AND THEY ARE TMOBILE OR IF YOU HAVE A NOTE 10 AND THEY HAVE AN S9.