When you say "I PM'd you", it's not clear, so, I think, Twitter, by choosing the...

kolev on Aug 13, 2015 | parent | context | favorite | on: Removing the 140-character limit from Direct Messa...

When you say "I PM'd you", it's not clear, so, I think, Twitter, by choosing their own term, it uniquely specifies the communication channel, i.e. you can PM via different channels (like Facebook, etc.), but you can DM only via Twitter.