I just figured out how to do this and I wanted to share it. This definitely works with Google Calendar, but theoretically can work just as easily with any .ics calendar hosted on the internet.
Okay, so you have your calendar on your phone, but you want to know what someone else is doing or stay in touch with some organization you’re a part of. Well. you can have access to both on the same calendar function on the iPhone.
Step 1: Get the .ics file for your desired calendar
In Google Calendar, tell you friend/association to go to Settings >> Calendars >> [Name of Calendar] >> Calendar Address: ICAL
Step 2: Copy the resulting URL ending in .ics and email it to your iPhone
Step 3: Find email and copy the URL
Step 4: Enter Settings on the iPhone and click on “Mail, Contacts, Calendars”
Step 5: Select “Add Account”
Step 6: Select “Other”
Step 7: Select “Add Subscribed Calendar”
Step 8: Paste desired URL and press “Next”
Step 9: Add a name and Press “Save”
Step 10: Press the HomeButton and Enter the iPhone Calendar. Click on the “Calendars” button in the upper left hand corner and you’ll see your new subscribed calendar.
Apparently, if you don’t have a MacOSX running iCal, you can’t customize the colors of the calendar, but if anyone finds a work around for this, please let me know.