It feels a lot more natural if you're sitting right next to someone or just around the corner. You can peek and make an educated decision of whether they look busy or not.
If it's a call it's a bit out of the blue. Maybe they don't have their headset around/plugged in, maybe they're doing something like eating or doing laundry. You just don't know because all you see is an activity status icon.
I still feel sending a message for 'if we can have a quick call' is still similar to being out the blue. I feel like I'm putting pressure on someone at this time.
- I either wouldn't see it because I'm involved in something out and messages are not priority interrupts. (i.e. I don't have notifications turned on.)
- Or, if I see it but now isn't a good time, I'll reply something like sure but right now is a bit crazy. Call my cell at xPM. (Or I'll drop something on your calendar.)
I have one coworker like that. It turns out that we're not able to schedule it until near the end of the day and it's just a simple question that could have been typed by them and answered by me far sooner had they typed the question instead of can we have a quick call.
If it's a call it's a bit out of the blue. Maybe they don't have their headset around/plugged in, maybe they're doing something like eating or doing laundry. You just don't know because all you see is an activity status icon.