Taiwan’s Ambit Microsystems has launched commercial 4G service and is the first operator in the country to offer Voice over LTE (VoLTE).

Ambit is the sixth 4G operator in Taiwan, which has a population of 23.4 million.

VoLTE calls are interoperable with Asia Pacific Telecom’s and Taiwan Mobile’s networks to start with. Ambit is reportedly in talks with Chunghwa Telecom, Far EasTone Telecommunications and Taiwan Star Cellular to expand VoLTE service to their networks, DigiTimes reported.

Ambit said it is offering unlimited internet access, free intra-network VoLTE calls and text messages, and free inter-network VoLTE calls for 1,000 minutes for TWD998 ($32.60) a month.

DigiTimes noted that about 170 VoLTE-enabled smartphones models have been launched globally, but only a small portion support the 700MHz band. Ambit said it has asked US-based vendor InFocus to upgrade its M810 smartphone to support 700MHz.

Taiwan Mobile said in December it planned to launch VoLTE in Q1 and was working out pricing strategies and roaming fees, but it has not yet made a formal announcement. Rivals Chunghwa and Far EasTone said they are preparing to launch VoLTE but haven’t finalised their plans.

Ambit and Asia Pacific Telecom (APT), both subsidiaries of electronics contract manufacturer Hon Hai Precision, two weeks ago announced they were investing an estimated TWD2 billion ($65 million) in a combined 4G network.

In late February the country’s telecoms regulator rejected a proposal to merge the two companies because they failed to provide details on a strategic alliance with Taiwan Mobile.

The rejection came just days after the country’s National Communications Commission said it was investigating complaints by three rivals of APT and Taiwan Mobile that the two operators’ 4G roaming agreement was illegal. The three complained that APT was using Taiwan Mobile’s network and had not built its own 4G network.

Ambit joined the 4G race in 2013 when it paid TWD9.18 billion ($312 million) for two licences in the 700 and 900MHz bands.