We will be releasing Remindo Push, but since it requires us to setup an infrastructure to push notifications to apple, it will be a monthly service (using the subscription payment api's from apple).
Since 37signals graciously offers us free accounts that provide sms and email reminders, Remindo standard can be a pay once work forever kinda deal.
One small suggestion - "Powered" is misspelled in your title ("Powerd [sic] by Basecamp"). I hate to be pedantic but it kinda jumped out at me - being a title, and all.
Would it be better to hold off until the 3.0 release for push notifications, thereby freeing you from creating the infrastructure for SMS and email?