Activate the External Calendars Add-on
Login to your ServiceM8.com account, go to the Settings menu, then click the ServiceM8 Add-ons button
Activate the External Calendars add-on by clicking the switch.
Configure External Calendars
Click the Settings button to get your external calendars URL
Each staff member has their own calendar url, you will need to repeat the process for each staff member's schedule you wish to see in Google Calendar.
Select and copy the entire URL for the relevant staff member.
Configure Google Calendars
Sign into your GMail or Google Apps account, and open your Google Calendar
Click the Other Calendars down-arrow, and click Add by URL.
Paste the URL you copied in the above steps, and click Add Calendar.
That's it. You should see your ServiceM8 schedule appear in your Google Calendar in the next few minutes, repeat the process for each staff member's schedule you would like to see.
NOTE: You are not able to make changes to your ServiceM8 Schedule, only view it. To make changes you must use the ServiceM8 Dispatch Board, or the iPhone/iPad app. Also be careful of recent changes, as while the Google Calendar is kept in sync with your ServiceM8 Schedule, it's not real-time - so recent scheudling changes may not appear in Google Calendar.