Downloading a .ics file from a url without opening the browser?
Go to http://www.google.com/calendar (on a desktop computer) and login with the same gmail as your phone.

On the left hand side bar there is "Other Calendars".  Click the drop down to the right of that, then choose "Add by URL".

In the modal dialog, enter the URL of the .ics calendar file.  Then click Add Calendar.

Now open Google Calendar app on your phone. Hit the menu button --> More --> Calendars.  You should see the email you just added under your gmail account.  Enable syncing for it and then hit OK.  You should now have the most up to date copy of that calendar on your phone.