If you've got a list of check boxes or radio buttons, sometimes you might want to give respondents the chance to add their own answer, in case their answer wasn't covered by the supplied options.
What type of mobile/cell phone do you use?
- Other (please type here)
Your respondent can select 'Other' and type their own answer right there.
You can activate this in the Properties of the question, just switch on the 'Other Option' switch for that Answer.