There’s no shortage of ways to communicate in the smartphone era, but most of them don’t involve actually hearing someone else’s voice. A Boston startup has landed investor backing for the idea that actual phone calls still have plenty of life left.

“You have to talk for business. You have to talk for family. It’s not going away,’’ said Peter Rinfret, the chief executive of ­Flyp. “I can’t believe we’re going to a world where people communicate only by the written word.’’

Flyp’s app lets users add multiple phone numbers to their cellphones, giving them the ability to route several types of calls through one device — personal calls on one line, business calls on another, and maybe even international calls on a third.

The company has raised $5.8 million in seed investment so far, Rinfret said, and is using the money to expand its base of about 20 employees in Boston and Dallas.

Flyp said its app has been downloaded more than 1 million times in the past nine months.

Pricing differs by country, but the US plan offers a limited number of minutes for free, charging for additional phone numbers and unlimited minutes.

Flyp’s app ties into traditional cellular networks, which gives the service a quality edge over Internet-only tools like Google Voice or Skype, Rinfret said.

And because Flyp’s phone numbers are all US-based, users can call internationally without incurring huge charges, he said.

In part, that’s possible because as smartphones get more features, carriers of all stripes are making less money from phone calls and texts. In response, those companies are moving their businesses toward charging for data use and giving away more voice and basic texting services.

In the United States, that tipping point occurred in the fourth quarter of 2013 — the first time that data revenues exceeded voice-call charges for American wireless carriers.

“We are migrating so fast to a universal talk-and-text world,’’ Rinfret said. “I remember when making a phone call from Manhattan to New Jersey across the river was a long-distance call.’’

Currently, Flyp is available in the United States, Canada, and 15 countries in Western Europe, Rinfret said.

It plans to expand to another 30 countries this year.

Curt Woodward can be reached at curt.woodward@globe.com. Follow him on Twitter @curtwoodward.