Mobile phone users: do not despair. Wireless companies say they are ready for Isaac.

In this cell phone-dependent age, staying tethered to mobile communications is vital, particularly during and after a storm.

Nationwide, six times as many AT&T customers have wireless devices compared to conventional land lines. And at least a quarter of Florida adults were living in wireless-only households in 2010, according to a statistical study by the Centers for Disease Control.

Since South Florida was last walloped by a hurricane when Wilma blew in from the west in 2005, providers like AT&T, Verizon Wireless, T-Mobile and Sprint Nextel have collectively invested billions of dollars to beef up their networks and cell sites.

And while no company will guarantee that its service will not be disrupted, each company says it has done all it can to prepare.

“People should be very confident because we have prepared and we have the response team that is battle tested and ready,” said Verizon Wireless spokesman Chuck Hamby. “Between the preparations and experience, we are confident.”

Verizon Wireless invested $138 million in network enhancements in Florida during the first six months of the year, including the roll-out of its 4G LTE wireless services.

And since last hurricane season, the company has installed new in-building network systems at hospitals, government and emergency facilities and other locations statewide.

Verizon has hundreds of cell sites around South Florida, all with battery backup. Plus nearly 85 percent of them have generators as well, to maintain wireless communication.

“The batteries will last about 10 to 12 hours, then the generator automatically kicks in and can run for a week without being refueled,” Hamby said.

Verizon plans to arrange fuel delivery in case of a storm, and said it will have tankers in position to quickly arrive at a hard-hit area.

The company has also strengthened its network with five “super-switch” network processing centers, including one in Pembroke Pines that handles Broward, Miami-Dade and Monroe counties, Hamby said, adding that the centers are designed to withstand Category 5 hurricanes.

AT&T, for its part, has invested nearly $2.8 billion in Florida from 2009 to 2011, plus more than $400 million during the first six months of this year, said spokeswoman Kelly Starling.

Its network upgrades include new cell sites to improve network coverage, faster connections to enable 4G speeds, added spectrum capacity to support additional network traffic, and launching 4G LTE in cities across the state, including in Miami and Fort Lauderdale, last month, she said.

And disaster teams are at the ready for Isaac.

“Our goal is that we don’t lose service because that is what we commit to our customers,” said Kelly Morrison, senior technical specialist for AT&T, based in Denver.

AT&T is always at the ready for a storm, both Starling and Morrison said. The company conducts readiness drills and simulations year-round.

In South Florida, AT&T has four wireless switches in South Florida with built-in redundancy and generators. Hundreds of cell sites also are equipped with batteries and generators, and additional portable generators are ready to be moved into place, Starling said.

Similarly, T-Mobile operates Network Operation Centers to manage network traffic during any storm.

In the event of widespread power outages, the company has backup generators and fuel tanks for regional network switch operations, and fuel is topped off for all generators in the potential path of a storm.

T-Mobile said it recently purchased 1,000 additional small mobile generators to assist with backup power to be deployed nationwide, whenever needed, and has additional portable generators that can be moved into place.

Sprint Nextel is also ready for the storm, and will begin rolling in and staging back-up generators this weekend and assessing deploying disaster recovery teams, said spokeswoman Crystal Davis.

Sprint’s cell towers are built to withstand winds of 110 mph, and in areas where the threat of significant flooding is high, the towers are elevated, she said.

Some cell sites have permanent generators, while others will have portable generators rolled in to supply power once batteries have kicked in.

“We’re confident,” Davis said, “that our network can handle what the projected storm might be.”