The 6.2 billion dollar (around 55 billion kronor) deal is part of Ericsson’s strategy to expand its presence in wireless enterprise and broaden its global offerings, the company said.
The offer was unanimously approved by Vonage’s board of directors, it said.
Ericsson is among the world’s biggest telecom equipment makers, battling China’s Huawei and Finland’s Nokia in fields such as 5G networks.
At 21 dollars per share, the offer represents a 28-percent premium over Vonage’s closing price on the tech-heavy Nasdaq stock exchange on Friday.
Founded in 2001, Vonage offers IP voice telephony and has in recent years developed a cloud-based communications platform.
The company has 120,000 customers, allowing one million developers access to its API interface which accounts for 80 percent of its annual sales of $1.4 billion.