the specials don't show on the mobile website. i'm hopeful you can still checkin from the mobile website and that will count.
the amex website says:
>>>
Unlock
Once synced, check in on foursquare to unlock specials and load those specials directly to your Card. No coupons required and no need to show your phone to receive the discounts.
>>>
So, you should be able checkin with a Treo (my example) and have that "special" loaded onto your card. Just have to remember the places with specials yourself. mobile website also doesn't show your saved lists (unless they've hidden it well) so that's kind of a pain.