Back in August I tried using the electronic BP to enter the gate at SIN, when they ask you for your boarding pass before going through security.

I showed E-BP to the staff at the X-ray machine. She hesitated, and started looking in the direction of her supervisor. I asked if a paper BP would help. She said yes, because she wouldn't need approval for that.

Not sure if that's changed since, but my attempts at using a boarding pass on my phone with SQ have been far from smooth. (They have been very convenient flying intra-Europe though.)