Originally Posted by
enelym1978
I am crediting all the miles on SQ (I'm SQ*S). I show up at the lounge desk, make a super polite greeting and smile and ask politely "excuse me, I'm *G on another carrier (show him my A3*G card) but I'm crediting on SQ (show him my BP with SQ*S marked on it), would it still be possible to use the lounge? It's so late and I just want to get some refreshments".
"Mhhh usually you cannot do this Sir, but as an exception, I will allow you to use the lounge, enjoy!"
The real question is whether they swiped your A3 card. If no, then you got a freebee on SQ dime by being nice. If yes, then A3 will have to pay for your visit and then you might be in violation of the T&C (might, and who knows what the ramification will be).
As for showing the *G card - that is a no brainier and carry no costs associated with it, so it would be up to the GA to decide whether to let you in or not.