How can I grab a teammate's attention?

Pausing is not the best solution, as the other team can unpause the game if they feel so inclined (and often they do).

If you are playing 2v2 (or any team composition) without voice (either in-game voice, or a solution like ventrilo), the game is definitely more difficult. If you are friends with the person, it helps to establish a concrete opening strategy before the game, and then use small messages while you are macroing and once you see scouting information to decide how to progress into the mid and late games.

If you are doing team games with randoms, it helps to start trying to establish this as soon as the game gets started while you are still creating your first drones. You'll know right away if you are in it alone, or if you have a very cooperative partner based on how they respond.

Also, give control of your units! I can't tell you how helpful this is so that both of you can micro at the same time, or help the other player micro when you can't get off something to type to them quick enough.

As already stated in many situations it will suffice to ping (Alt+G click) the minimap.

Depending on how good your ally is and how often you have played with him I think the following is a good guideline:

• ping once - Look here, I want you to see this.
• rapidly multiple pings - Immediate threat, react fast!
• chat "scan", ping once - I want you to scan here.
• chat "100 min" or "100 gas" - Need 100 minerals or 100 gas.
• chat "gg?" - I have nothing, do you have anything that can change the game?
• chat "i go ..." - I will use ... strategy.
• chat "can i fast expand?" - I want to use the natural, can you cover me?
• chat "scout" - Send a scouting worker, I need my resources.
• chat "push" or "push?" or "push in x" - Asking when to push or indicating you want to push now or soon.
• chat "b" or "back" - You will not commit to this fight and want your ally to back off.

There are many other messages, but these are the ones I use most often.

You should rely on common sense and trust your ally. Assume that if you show him something he will react correctly.