Jerrad

Are there Any apps that can facilitate communication between two or more phones by just using their radios with out cell towers or the internet? I understand there would be a limitation on range but I assume it would be better than walkie talkies and always in your pocket. Then their is the possibility of implementing a mesh network to increase range. How difficult would it be to write software for this?

So I was looking at getting the Ulefone Power 5 but I noticed on US carriers it is only compatible with x1 4G & x2 2G bands with no compatibility for 3G on Verizon. Other carriers were simular or worse. Are more than one band in a generation class necessary for good cell phone reception and fast download speeds? I.E. With the 4G/2G compatible bands stated above would I notice missing other bands? This leads me to my next question. Has anyone unlocked a phones radio bands through hardware or software modification? Or since this may or May not be legal in your country, theoretically how could it be done?