Loudtalks is now Zello. Check out www.zello.com
Now we are talking
Lightning fast push-to-talk between Android, BlackBerry, Windows Mobile, PC and two way radio
Connects in under a second
Group calls for up to 1000 users
3G or WiFi
Any carrier, worldwide
No contract
Free version is available
Loudtalks Lite
Instant voice communication for personal use. Great to keep in touch with friends, family or online game teammates.

Use Loudtalks Lite for Android, BlackBerry or Windows Mobile to turn your smartphone into real walkie talkie!
Free
Loudtalks Mesh
Push-to-talk for the enterprise. The complete client-server solution, which you can deploy at your organization's network. Up to 1000 users per call, web-console for users, channels and access rights management, integration with two-way radio and PA systems are some of advantages of Loudtalks Mesh.
From $9,000
Loudtalks Cloud
Loudtalks Cloud is a hosted version of Loudtalks Mesh. Just sign up online, download a client application and you are all set. Streamline your work communications with no upfront investment.

Better yet is that Loudtalks Cloud is free for up to 5 users so you can fully evaluate it before buying.
From $4/user per month