Zer01 is taking on AT&T (NYSE: T), Sprint (NYSE: S), T-Mobile, and Verizon (NYSE: VZ) Wireless by offering unlimited voice, text, and data plans for $69.95 a month with no contract or credit check.

The company is able to undercut the competitors by using a voice-over-IP client on the handset for all voice calls. This is made possible by interconnect, or roaming, agreements to use AT&T’s and T-Mobile’s networks to tunnel to Zer01’s IP backbone. For an extra $10 a month, users also will be able to make unlimited…