SPA-841 & *: how to forward callwaitng to second line?

[anatoli]

I can't figure out how to utilize a second line for call waiting.
Here is what I mean:
PSTN has a callwaiting feature, I'm on the SPA-841's line1 talking via * to PSTN callee, I'm getting callwaiting beeps - somebody is trying to reach me via PSTN. I'd like to press Line2 and talk to a new callee, then return to callee1 pressing Line1.
At work we run Aspect PBX, so if I'm on the phone I see a second line button starts flashing if somebody calling me. Pressing a second line button puts a first line on hold and vise verse.
Can I do the same with * and SPA-841?

Actually to flash PSTN line from SPA-841 is also not so trivial