Here is how they are getting away with it (direct copy from their website):
Answers to your questions:

1. I'm on the Do Not Call list so why did you call me?
The US Federal Do Not Call List and the Canadian Do Not Call List apply to telemarketers, telemarketing, and sellers or promoters of goods and services. SSI only conducts legitimate marketing, survey, and opinion research and is therefore excluded from coverage.
2. How long does it take to remove my number from your lists? Will I get any more calls from you?
It will take up to 5 business days to process and remove your number from all active survey research projects. We apologize if you receive any calls during this period.
3. Can I change my mind in the future?
We will be happy to welcome you back in the future. Simply send an email to info@surveysampling.com including your telephone number.
4. Who is Survey Sampling (SSI)?
Survey Sampling International (SSI) is a company which helps researchers listen to and access people's opinions. SSI is a member of the Council of American Survey Research Organizations (www.casro.org) and complies with research industry standards, best practices and relevant laws. SSI believes that legitimate research is a vital part of society because when people give their opinions, they can help shape, improve, and create products, services, programs, and policies that impact people, society and the world we live in.
5. Why did you call my mobile number?
SSI understands its legal obligations restricting the use of autodialers for wireless calls absent permission from the recipient. We have designed a proprietary industry-leading platform to ensure we comply with such obligations.  However, we respect your preferences, please refer to the ?opt-out? instructions above.
We appreciate your participation in our research and we value your opinion. But if you do not want to participate in the future, we of course understand and respect your decision. To opt-out, please email us at optout@surveysampling.com (please include the phone number in the body of the email.) To opt-out by telephone, please call 1-866-360-9563 from within North America or 1-801-379-4094 outside North America to be placed on our no-contact list. If you would like to speak to someone about the call you received, you may contact us toll-free within North America at 866-360-9678, or call 1-801-379-4094 outside North America.
http://surveysampling.com/en/general/received-a-call

A survey company.  If you call, the message tells you to learn more at their web site, at surveysampling.com .  I went there and there is an opt out button, which opens an outlook message with this address: optout@surveysampling.com
I just tried it and only time will tell if the calls stop.  I used my junk mail e-mail address, because I wouldn't be suprised if I start getting tons of extra junk e-mail/spam.
Chad

Caller ID ..SSI...social security ??   Answered this call...no one on other end..?

Survey company.  Just ask them to kindly pound sand, and they will.

Today, 303-219-7034 and yesterday, 303-330-0000.  Too much for me, legitimate or not.  Adding them to my black list for peace and quiet.

I just got a call from this number on May 3, 2014 at 8:27 PM.  The caller ID read SSI.  When I answered, it was silent for a moment, then a single beeping noise, and then the call disconnected.

SSI data collectors, keep calling me late at night and waking my kids up.  You pick up the phone, and it just beeps, noone is there! This is from their website:
We appreciate your participation in our research and we value your opinion. But if you do not want to participate in the future, we of course understand and respect your decision. To opt-out, please email us at optout@surveysampling.com (please include the phone number in the body of the email.) To opt-out by telephone, please call 1-866-360-9563 from within North America or 1-801-379-4094 outside North America to be placed on our no-contact list. If you would like to speak to someone about the call you received, you may contact us toll-free within North America at 866-360-9678, or call 1-801-379-4094 outside North America.

SSI offers an opt out option via email or telephone.

http://www.surveysampling.com/en/general/received-a-call

Good luck.

Just called my number in Denver, no message. ID says "Brighton Colorado"

P/C f: 303 219-7034 @ 4:55PM 12 April 2014, @ 7:41PM on 11 April 2014, @ 7:21PM on 10 April 2014, caller ID indicated SSI with the phone number of 303 330-0000.  SSI = Survey Sampling International.  www.surveysampling.com.  Below is a cut and paste of their propaganda.  I believe they are Data Collectors.  Who D hell R these people?

"SSI provides sampling, data collection and data analytic solutions for survey research, reaching respondents in 86 countries via Internet, mobile/wireless, telephone, and mixed-access offerings. Staff operate from 25 offices in 18 countries, offering CATI, questionnaire design consultation, programming and hosting, online custom reporting and data processing."

I got this call again at 8:11 PM tonight on April 9, 2014.  I picked up, said, "Yeah?" and it was a beep noise and  the call disconnects.  The caller ID just reads the number as the display name.  I do not know who these people could be.

4/7/2014 ....they guys are a bunch off low life. They call I answer and they keep asking for a person that rented a room here 2 yr ago.i told them that if they keep calling here I will call the police. They now stop calling.

This number called me last night,it was some dumb political survey! About Obamacare and all that! It made me angry.

I got a call from this number at 7:55 PM.  The caller ID just displayed the number as the display name.  When I answered, I did not say anything.  I heard a beep and it immediately disconnected.  I did not get a call back.

These idiots called asking for my wife who passed away over two years ago.  How can we get these types of calls off of the internet?

They also have a Facebook page Survey Sampling International (SSI)

This appears to be a legitimate survey research company located in Brighton Colorado.  They have a website and a voice message answers the phone when you call them back. The website is  http://www.surveysampling.com/

This number called three times in a row. Never left any message. I did not answer any of them. But my phone said they were located in Brighton Colorado.

Called at 9:45 pm. No solicitors are allowed to call after 9 pm. Told them to remove me as I am on the do not call registry.

Asked for the adult of the house...would not identify self. I asked them to take me off their call lust...female just hung up & called 10 minutes later...the second time she hung up as soon as I answered.

Recorded message from Carpet/Air Duct Cleaning, Furnace tune-up scammers.  Talked to them once.  Told them to come over and I'd load up the 12-gauge.

Caller ID said SSI.  Don't know who that is so I didn't answer.  Only rang twice - voice mail picks up after 3 full rings.  I read other comments where people think it must be Social Security but they are SSA, not SSI.  They also would not call at night.  Got to assume it's a scam.  

missed the call

Whoever this is called me twice within 15 minutes.  Caller ID says SSI, which made it seem to be an entity of the office of Social Security.  However, since they call me at 8:00 p.m., and knowing that no lazy government employee from SS would ever work past 4:00 p.m., I decided not to answer.

Second evening call from this #, labeled "SSI" on callerID.  2nd time I answered, then a hangup.