In Google Analytics you can separate data by device category (desktop, tablet, mobile).
Depending on what you're measuring, you may want to combine data for tablet and mobile.
In the advanced filtering options for Google Analytics, filters are joined by AND and this cannot be changed to OR.
However, you can use regular expressions to accomplish the same thing.
In the 'Reporting' section, view a report for a dimension (for example, on the left-hand side, select Audiences followed by Technology followed by Browser & OS).
There should be an 'advanced' option (at the time of writing it is located next to the search field). Click it and set the value for Containing to /(mobile|tablet). This will exclude data for desktop browsers.
This is a quick and throw-away method. If you want the filter to persist and configure it further, see Creating persistent device category filters in Google Analytics.