Law firms in the United States and Canada are considering possible consumer lawsuits against Research In Motion Ltd for last week’s BlackBerry outages, which for three days crippled email and messaging for tens of millions of users around the world.

Consumer lawyers say they are investigating whether customers have common claims against the BlackBerry manufacturer and might be able to band together in a single lawsuit.

While the outage did not rise to the level of seriousness comparable to a dangerous medication or tainted food, it inconvenienced and angered customers. Frustrated BlackBerry users, turning to blogs, message boards, Twitter and Facebook, complained about losing important emails and missing meetings last week.

Law firms are considering breach-of-contract or consumer-fraud claims, attorneys said.

A breach-of-contract claim could argue the company failed in its obligations to provide service and could include carriers for BlackBerry service as additional defendants, said attorneys exploring litigation against RIM.

A consumer-fraud claim could focus on whether customers were misled about the reliability of RIM’s networks.

But consumers could face hurdles to winning big damages. It will likely be difficult to prove damages beyond loss of service and varying state laws make the chances of bringing a nationwide consumer-fraud class action remote.

Still, lawyers are investigating whether plaintiffs could band together and what claims they could file.

RIM did not respond to messages seeking comment on potential lawsuits.