The number of households in the United States that rely solely on wireless telephones continues increasing. More than one in four households had cell phones and no landlines in the first half of 2010, which is an increase of 2.1% since the second half of 2009. And almost one in six households uses cell phones exclusively or almost exclusively despite still having a landline.

What’s most interesting is that more than half of adults between 25 and 29 rely on cell phones alone. This is the first time that adults of any age range have been more likely to go without landlines. This trend indicates that those who have grown up with mobile phones as an accoutrement that went along with their lunch box have never bothered to get a landline. In a few decades, the landline will probably be about as obsolete as the rotary phone is today.

As a result of this shift, software application developers are focusing primarily on mobile devices, with PCs demoted to a secondary consideration.

And whenever there’s a major transition to a new technology, the uncertainty and newness creates the perfect opportunity for scammers to launch attacks. Dave DeWalt, chief executive of McAfee Inc. security software, predicts, “2011 is the year of the threat to the mobile device, particularly the mobile app.”

There are plenty of new tablets and smartphone devices coming out this year, along with thousands of new mobile applications. Meanwhile, hackers are creating bugs and viruses that modify the legitimate software industry’s processes.

Expect more scams and more scam warnings in 2011. The main initial concerns involve rogue apps and phishing messages designed to extract credit card numbers and login credentials. As mCrime evolves and criminals begin to make some money, they will have the resources to hire crackerjack programmers to do their deeds.

Robert Siciliano, personal security expert contributor to Just Ask Gemalto, discusses mobile phone spyware on Good Morning America. (Disclosures)