Dual mode mobile phones capable of both VoIP over WiFi and GSM over traditional networks are poised to become "the next big thing." Frequent travelers and frequent talkers alike will be able to benefit from cheaper phone service provided by VoIP when WiFi networks are available, while not giving up the flexibility and broad network coverage of a traditional mobile phone. The VoIP cost saving aspect becomes all the more important when international travel is considered, as bringing your GSM phone abroad can cost you upwards of US$2 per minute in calling charges.

Here, we take a look at some of the best new offerings in GSM VoIP phones:

First up is the Calypso C1250i, with built in 802.11 wireless capability, allowing for not only VoIP audio phone calls, but when teamed up with its 30 frames per second video playback and recording functionality, live action video phone-to-phone video conferencing as well.

Also notable about Calypso Wireless is its “Automatic Switching of Network Access Points” technology which allows seamless voice roaming between GSM cellular networks at WiFi networks.

Next up is Voice Internet Phone Network’s (VIPN) Axia 308. This quadband GSM phone also supports GPRS, 802.11 WiFi, VoIP, and is a PDA running Windows CE. The phone will sell for around US$600.

Finally, Paragon Wireless introduced the first dual mode SIP phone in China this week – the PWTW-1100. The handset boasts a four hour talk / 72 hour standby battery capacity, even when both its WiFI and GSM capabilities are running. It also offers an SD memory card slot and an MP3 player, giving it iPod like functionality. And in terms of security WPA encryption and a VPN (Virtual Private Networking) client are included, as well.

These are some of the hottest VoIP GSM dual mode phones, but clearly they’re not the only ones. Anything better out there that we missed? Post a comment.