In most cases, the TEXT field type should be fine, but it would be nice to be able to have a custom field type of numbers only.
For example, the company I was using Matukio for has staff code the start with letters, then numbers following. What they wanted me to do is create a field that the registrant needs to choose their starting letters, then the text box would only accept numbers.
For example, the number only box would accept 1234, but not ABC1234