Vonage said its VoIP calling applications for the iPhone and BlackBerry platforms are now available.
The apps use cellular networks to connect with Vonage's VoIP infrastructure to enable users to make lower-cost international calls to mobile phones or landlines. The software integrates with the handset's contact lists. Apple users will be able to make calls over Wi-Fi and cellular networks, and BlackBerry users can only use cellular networks.
The apps are free to download, but an unlimited calling plan costs $24.99 a month. Existing Vonage customers can receive a $10 discount when using Vonage Mobile.
"As mobile devices become more powerful, broadband networks become more available and 3G/4G data networks become more open, we envision a future where Vonage delivers calls, readable voicemail, texts, MMS, and video calls from any device, using any broadband connection," said Vonage CEO Marc Lefar in a statement.
The calling app can be downloaded to the iPhone and iPod Touch via Apple's App Store. The BlackBerry version of the app is available for download from vonage.com and via Apple's App Store.
The move is another sign that mobile operators are becoming more comfortable with VoIP-like services on smartphones, even though these have the potential to eat into voice revenues. AT&T recently said it would enable VoIP programs to operate over its 3G network and this could lead to wider adoption of services such as Skype on mobile phones. VoIP providers have said the potential revenue carriers lose with voice minutes can be offset by the usage of mobile data.