I theorize that it's 2. I log into Paint on my PC and on my DSi. Absolutely no issues there. However, if I try to use a third device, like I did with my phone, it logs off one of the devices, I think. All I know is that my phone logged in and afterwards, my DSi logged out.
I want to know if this is the case. I haven't looked at the relevant source code, though. Just wsnted to ask if other Helpdeskmins have their owntroubles with this.