It's SSI (Survey Sampling International). It's one of those "pay for your opinion" companies. I find them particularly unethical because in some cases the caller ID reads SSI and some folks believe it is the Supplemental Security Income (Social Security) calling and therefore are more likely to answer. Here are some complaints about them:
http://www.ripoffreport.com/reports/specific_search/Survey+Sampling+International%2C+LLC