So says David Goldman in a piece a month ago (late to the party I am) on CNN Money.

Wi-Fi is ubiquitous. No longer the realm of coffee shops and homes, Wi-Fi spans entire neighborhoods. Trains, planes and automobiles are Wi-Fi equipped. Cruise ships have Wi-Fi. Comcast (CMCSA) has even made every customer’s router into a public Wi-Fi hotspot.

That’s good news if you’re a cell phone user. The more you email, watch Netflix (NFLX, Tech30), stream Pandora (P) and surf Facebook (FB, Tech30) over Wi-Fi, the fewer gigabytes you have to buy from your cell phone company. Plus, calls and texts are now able to be sent over Wi-Fi too.

Broadband customers that actively use Wi-Fi on a regular basis save more than $30 per month on their wireless bill, according to a Macquarie Group survey published last week.

Don’t cry for the mobile carriers, they still have many profitable years ahead. Before going all WI-FI, you will want to be sure that hot-spots get more secure, too. Still, it is is a sign of the times that carriers like Verizon are reducing the bandwidth for 3G service and shifting it use by 4G.

The bottom line: Don’t be afraid to switch to save bucks.