For years, cellphone users have accepted a frustrating reality: no matter how advanced wireless technology becomes, dead zones still exist. Whether traveling through rural backroads, hiking in national parks, boating on remote lakes, or even driving through pockets of suburban sprawl, losing signal has remained a common annoyance — and sometimes a dangerous one.

Now, the nation’s three largest wireless carriers — AT&T, Verizon, and T-Mobile — are taking a major step toward changing that reality.