Free 45 minutes of Boingo Hotspot access from American Express:!
Cardholders are validated by selecting their card type - and then putting the customer service phone number from the back of the card.
Here's Blue from American Express:
I don't know if you can mix and match AMEX cards to earn more time or if you can stack the 20 minutes for everyone on top of the 45 minutes for cardholders. I'll allow crowdsourcing to find that out for me.
Enjoy free surfing!