In theory, the feature enabled parents to block calls to and from a wireless phone at a time of their choosing. A special list of "Allowed Numbers" (the parents’ phone numbers in most cases) and emergency 911 calls were to be excepted from this rule.

However, it turns out that while the child would be able to call 911, the a emergency operator was not be able to contact back the caller, if the original call would be terminated for some reason.

It’s interesting to note that this issue was discovered during one of AT&T’s test, but hasn’t been reported by customers.

For the time being the Smart Limits service will only allow parents to filter access to Internet content they consider to be inappropriate for their children and set a limit for download purchases, such as ringtones and games.

The company stated that the “Allowed Numbers” feature would become available once again “as soon as possible”, but didn’t provide a specific time frame.

The program was launched on September 4 and charges $4.99 a month.