(Also see Mary Ellen Foster’s comments on this post below).
There have been very recent changes to how Wireless@SG registration works. As reported in the conference handbook and earlier on the website, international phone numbers used to be accepted for registration — this is no longer the case.
Registration confirmation and password are sent via SMS; local Singapore mobile phone numbers are required at the moment. We advise you to purchase a prepaid SIM card upon arrival to Singapore. The prepaid SIM cards for all 3 mobile operators are sold in a number of shops including convenience stores like 7-Eleven. Passport is required to purchase a SIM card. See the earlier post about hand phones for more information on obtaining a SIM card.