UK-based mobile VoIP player Truphone has closed a second round of funding worth £16.5 million (US$32.7 million) to help build-out its core GSM network. The news comes just days after the company announced it had acquired SIM4travel, a Mobile Virtual Network Enabler (MVNE) platform with travel SIM capabilities.

The latest cash injection was led by private investors, with all of Truphone’s existing backers – Burda Digital Ventures, Eden Ventures, Independent News & Media and Wellington Partners – participating. The company raised £12.5 million in an earlier round of funding last year.

The company plans to enable low-cost GSM calls worldwide using the travel SIM in tandem with its existing mobile VoIP service, which works with high-end devices such as Nokia’s N-series and allows free calling between Truphone users. Truphone aims to disrupt the existing mobile marketplace by offering cheaper international calls than the established mobile operators.

The company’s infrastructure incorporates a global network of SIP gateways, a Nokia Siemens Networks mobile network Home Location Register (HLR) and a GSM identifier. The infrastructure is capable of supporting 40 million customers worldwide, Truphone says.