In a web survey you see a free text question as a field where the survey participant fills in his answer.
Designing the survey, you can set the allowed amount of rows the survey participant can write in, at the bottom of the free text question form.
Free text questions can be used in surveys sent out as sms.
Free text questions cannot be answered in telephony survey but should you want to include free text questions in a survey that will be used for both web and telephone, you can. Then the free text question will just be skipped in the telephony survey.
Technically, each sms can only contain 160 characters. If your text exceeds the limit, multiple sms' are sent out. On the recipient's device the sms' are merged again, showing your text as one single message. You just need to know this as you might be charged for the actual amount of sms' sent.