It's been a while coming, but Verizon this week finally flips the switch on Wi-Fi calling, kicking off on Tuesday with the Samsung Galaxy S6 and S6 Edge handsets.

The company says users of other devices won't have to wait too long to join the party, promising a wider rollout for additional Android smartphones as well as iOS handsets "early next year."

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The feature enables a handset to automatically switch to an available Wi-Fi connection -- this could be at home or in a public space with Wi-Fi like a cafe -- when it detects that the cell signal is too weak to maintain a decent connection, or if no signal is available.

Such a service should come in useful for anyone who finds themselves in a place with a lousy or unreliable cell signal, which could be the result of being in an out-of-the-way location or due to a building design that reduces the effectiveness of the signal.

Verizon is offering its Wi-Fi calling feature as part of its "Advanced Calling" voice-over LTE service. The company said in a release that all Wi-Fi calls made to U.S. phone numbers will be free, while calls made to foreign numbers will be billed at international long-distance rates.

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Verizon CFO Fran Shammo said last year the company had been cautious in rolling out Wi-Fi calling because call quality is out of its control and dependent on the Wi-Fi connection. Since those comments, AT&T, T-Mobile, and Sprint have all started to roll out their own Wi-Fi calling services, with Verizon evidently reluctant to hold off any longer.

Verizon customers with a Galaxy S6 or S6 Edge device can get started with Wi-Fi calling by downloading and installing the latest software update and turning on Advanced Calling from the settings menu.