Heavy spending across the United States, China and Japan lead the global VoIP and IMS markets to grow 30 percent to €2.7 billion in 2013.
According to new research from Infonetics, Huawei, Alcatel-Lucent, Ericsson and NSN each saw their fourth quarter revenues increase by more than 20 percent on the previous year.
Diane Myers, Principal Analyst for VoiP, UC and IMS at Infonetics, said: "Though there's still room for pure-play vendors and product specialists, the large equipment manufacturers benefit from long-standing relationships with mobile operators and broad product portfolios that extend well beyond carrier VoIP and IMS."
However, Infonetics predicted spending would taper off during the next 12 months as operators start to launch services and draw down inventory.
In September, Telefónica Germany signed a deal with Oracle for it to provide several services, from VoLTE, residential VoIP and RCS-e across one platform.
Last month, the Global Mobile Suppliers Association said it expects VoLTE services to grow this year, with more than 30 phones on the market that are capable of using the service.
In separate research, Juniper said last month that operators could achieve sales of €14.7bn by 2018, thanks to the implementation of strategies including VoIP and so-called "carrier OTT" services. However, it said that adoption will be driven by the network efficiency that it will achieve, rather than a direct boost to sales.