Depending on your source, the potential damage this flaw could cause varies. Some go so far as to claim it could let remote users make calls with your phone, pilfer data from it or even more. What makes it especially scary is that it can be spread completely via SMS messaging, requiring no intervention on a user's behalf. An iPhone can be compromised through specific crafting of malicious text messages, most of which would be hidden to the victim.
Though unofficial patches have reportedly surfaced, there has been no official response from Apple on what the flaw entails and how long users will have to wait for a fix. I wouldn't personally suggest installing third-party software, and would instead hope that Apple comes up with an official response – either dispelling this as hyped nonsense or confirming it as a danger and offering a solution. Interestingly, one of the most plausible-sounding do-it-yourself fixes requires having a jailbroken iPhone, which can let you disable the messaging application on the iPhone without removing it.