WhatsApp has announced that the introduction of its voice-calling feature has been delayed until early next year, Digital Spy reveals.

The ability to make and receive calls over WiFi was expected to be added in the second quarter of 2014, but Jan Koum revealed the postponement at the Code/Mobile conference this week.

Koum said that technical difficulties are behind the delay, including the problem of the app being denied access to the microphone on some handsets.

WhatsApp was acquired by Facebook in a big-money deal earlier this year, and the social network already operates its own Messenger app, a service that already includes voice calling over WiFi.

However, Koum insists that the two applications are not in competition with each other and envisions them coexisting harmoniously.

Earlier this week, Facebook announced its quarterly financial results reporting a heavy increase in expenses due to its purchase of WhatsApp and other costly acquisitions.