These guys are not telemarketers and they only call if there is a legitimate reason, usually technical, like your site or services are down. If they have your number in error, then that's something else... but they have no reason to call you unless you have an account with them to alert you about some issue in your service. Not sales or marketing.
this is Rackspace.com a website hosting service. they also have webmail service AND ICLOUD SERVICE. they are probably calling to verify information or to followup on your account. if you don't have a rackspace account then someone gave them your number by accident.
Rackspace not only had my phone number but also my credit card number! They tried to make bogus charges several times. I did not subscribe to their service at any time. They also called our home in the middle of the night. Luckily our credit card company caught the unauthorized charge attempts immediately and stopped them. A company who has one's credit card number in addition to one's phone number does not get that information by accident! This company has an illegal operation going on.
I have a server with Rackspace and in order to open an account you have get a quote and sign paperwork amongst other things. It sounds like somebody went through a lot of effort to use your information to open an account including signing your name on your behalf. What is puzzling to me is that they would use your actual phone number.