This picture (which comes to me from Failblog) nicely encapsulates two of the key challenges in collecting customer feedback:
First, you need to make sure your customers can actually take the survey. Many survey methodologies systematically exclude some segment of your customer base. Unless you account for that there's the risk you could be overlooking something important.
Second, you need to make sure the survey itself doesn't bias the responses, either through poor questions, or because the process (like in this case) annoys your customers.
For what it's worth, I had my own problems with an AT&T text message survey last year.
>> Process Bias