There is a site that allows you to see all SMS received by a certain set of phone numbers (owned by the site). This seems to be meant for services that require two-factor authentication using SMS, when you're unable (or unwilling) to provide your phone number for that SMS. Instead, you enter a phone number provided by that site and then use that site to view your authentication SMS.
Obviously, this decreases security, because it basically turns the two-factor authentication back to one-factor (because that phone number is not “something you own”). But apart from that, is such site safe to use? Could they somehow use the received SMS to get access to my account, or for some other nefarious purpose?
For the record, the site I'm talking about is http://receive-sms-online.org/.