Baby Monitor 3G normally R68 now R6, works really well, handy even just for the streaming video/screenshot feature with walkie talkie to use whenever that's needed:
https://play.google.com/store/apps/details?id=com.tappytaps.android.babymonitor3g&hl=en
Interesting feature is it is cross platform you can mix Android devices with Apple:
https://itunes.apple.com/us/app/baby-monitor-3g/id490077681?mt=8
Seems the app only works via the internet(via 3g or wifi) so essentially you could have the 2 devices connected that can be separate and anywhere in the world in different geographic locations, also means it can be used on the go anywhere no wifi network needed, suppose for some folk that may be a drawback ie you use data.
The app must stream via their servers?
To connect 2 devices you just input the code given by the one on the other device, both then see each other, both connected via 3g only so no local discovery via wifi, also must be some server involved to achieve that?