There is an old post for this offer that expired in 2006.
Here's the new offer:
New Speedpass customers in FL, LA, MA, NC, NJ, RI and SC will receive a $20 ExxonMobil Cash Card (or a $20 ExxonMobil Credit Card statement credit if Speedpass is linked to an ExxonMobil Credit Card) for activating a new Speedpass account.
To qualify for one of these great offers, just enroll and activate online by December 31, 2008!*
Yes, you can link Speedpass it to any credit card.
Note - ignore the mailer sticker that says you should call into activate the card - you MUST activate on line after you receive your package to receive the GC or the rebate!