SGTM is an acronym you might have come across typically in conversations with texting or social media, for example.
SGTM is an acronym for "Sounds good to Me."
SGTM is used typically to agree with something. A good example would be if someone wanted to meet up with you at a set time or place. You can quickly respond with SGTM to agree.
SGTM dates back to message boards and Internet Relay Chat (IRC) as far back as the 1990s but didn't appear on Urban Dictionary until 2007, about the same time the smartphone (iPhone) was released to the masses.