I'm currently in a game with 4-member teams.  One of them just sent me a PM asking me to make a certain attack.

My first thought was to ask him to share that request with the other two team members.  My second thought was to post a request here for the means to PM all team members with one post in team games (as long as you're Premium and can send in-game PMs). 

Actually, it would be ideal if that was the default.  Whenever Player A PMs Player B, Player B sees it like normal, but Player's C and D also see something like "Player A messaged Player B: blablabla"

My apologies if this has already been requested, as I've admittedly not read every single previous post.

You can "PM" to all teammates.  It's listed as "Send a Team Message" or something like that and you get to it through the same drop-down list you use for PM'ing. 

The message shows up with a green background in your discussion area below the game.

Are team messages allowed for non-premium members?  I think they should be... even if they can't send private, they should be able to send team...

I'm pretty sure they can. ..or so my brother (who is a non-premium member) says.

Yes, everyone can send team messages.

Good