New mobile carrier Zer01 Mobile will offer $70 unlimited voice and data package that will utilize three of HTC’s phones–the Diamond, Touch 3G and the TyTN II. Customers can also bring in their own GSM-unlocked devices to the carrier, including the iPhone 3G in the future.

Zer01 works with roaming agreements on AT&T and T-Mobile in the USA and offers domestic unlimited for $70 and international unlimited to forty specified countries for $10 more, though none of the calls will be routed through GSM. All calls will be handed through a VOIP system on Zer01 servers. Initially, only Windows Mobile phones will be supported, though additional platforms will be added.

According to Electronista, A handset on the network is assigned a fixed IP address that provides a VPN tunnel to Zer01′s servers, where the traffic is managed to prevent overload on the cellular networks. “It’s our own VPN, and we’re actually providing the data the customer is using,” Piilani added. The company avoids data caps by using established interconnect agreements.

Although the company isn’t a mobile virtual network operator (MVNO) like Virgin Mobile in the US (which also acquired Helio) and the now defunct Amp’D Mobile, it is still dependent on towers from other GSM carriers in the US. It’d be interesting to see how the firm handles areas where AT&T has no 3G and service may fall back to EDGE or on a T-Mobile spectrum as current devices capable of AT&T 3G are not compatible with T-Mobile’s nascent AWS 3G network, and vice versa. Moreover, the proposition for low-cost unlimited data and voice may not exist other than network size due to roaming agreements as T-Mobile had recently begun offering unlimited voice for $50. Add on another $20 for data and you’ve got Zer01 matched for domestic calls and data. However, the international plan will be a cost saver for those who make frequent calls to any one of the forty countries supported by Zer01.

You can learn more about the plans and the startup at Zer01 Mobile.