This post will show you how to subscribe to your Basecamp calendar in iphone calendar.
For instructions on how to subscribe to your basecamp calendar in google calendar please see this post

Basecamp is a great way to keep track of lots of things in your projects. You can use it as a to-do list, you can use it as a way for your clients to submit change requests, you can reply in-line to their requests asking for more information, etc – you can also just reply to email that basecamp sends to you informing you of changes and basecamp will add the replies itsself, keeping everything in a central location!