Teles of Germany has threatened to sue Nokia for patent infringement over the handset maker's VoIP phone.
In a statement posted on the Teles Web site, the company claimed the Nokia 6136 phone's "GSM fallback" functionality infringed on the firm's patents.
Teles also said it intended to launch over the short term further patent infringement cases against internationally well-known providers of VoIP products with "line-switching fallback" functionality for fixed and mobile networks.
According to the statement, advanced VoIP products with support for packet-switching over the Internet violated Teles' VoIP patents, which it filed in 1996.
The company further said it had tapped the services of Washington-based law firms to handle possible VoIP patent violations in the US.