They definitely are keepers. I will have an update to post later tonight.
Sent from my XP8800 using Tapatalk
XP8800 phone model = XP8.
As promised, here is an update. I haven't had an opportunity to do any range testing yet but my wife and I were able to play around with Sonim Direct Mode a few times while we were out and about. The module and app does work as advertised but there are a few quirks to be aware of.
Unlike the Motorola DTRs and DLRs, the app doesn't wait to receive an acknowledgement from a receiving phone w/module before transmitting. It sends a burst of syncronization data immediately upon pressing PTT and then waits a little under a second before transmitting. The Talk Permit Tone (TPT) is a short beep upon pressing PTT followed by a 2-tone (lo/hi) beep about a second later. I found it continues transmitting even if there's no other phone w/DM module in range to receive the transmission. I confirmed this by looking at it with a spectrum analyzer. This is different from the Motorola DTR and DLR behavior which requires a radio to receive an acknowledgment from another radio in range in order to continue transmitting. The DTRs and DLRs are easy to test range with; you don't need another person to test with because you'll know if you are in range or not upon pressing PTT. You will get an error tone if a transmitting DTR/DLR radio doesn't receive an acknowledgement from another DTR/DLR radio in range.
I found it is best to use the Sonim Direct Mode app while in Airplane mode. The app has a "knife switch" setting to automatically put the phone in airplane mode when using the app. Normal network connectivity is restored upon exiting the app. I found using the app when NOT in airplane mode causes audio dropouts here and there. I also found the module to be sensitive to the state of charge in the battery. When the battery in one of our phones had less than about 10% charge, the module would frequently stop working and I would have to restart the app to reset and restart the module. The phone was not in airplane mode when I noticed this.
Audio is similar to using a PTToC app and sort of like speakerphone audio when in a voice call. I wish the audio were a little louder though. I want LOUD audio. The AT&T EPTT and Zello apps have louder audio. The Talk Permit Tone (TPT) and voice end tone beeps are less obnoxious than the AT&T EPTT beeps. The app volume is adjusted by the Media volume control on the phone (not the ringer or alarm volumes).
The module makes the phone about an inch taller when installed, not counting the antenna sticking up. I am finding the phone to be more comfortable to hold against my ear when a voice call. I previously didn't like the feel of the earpiece at the top edge of the phone.
The Sonim Direct Mode app is easy to use. The two general modes are channels/codes mode and talkgroup mode. In channels/codes mode, there are 16 available channels with 16 available codes plus a "none" code setting and a Broadcast (All) feature. Given the few channels and few codes available, my gut feeling is that it is not very secure. The specs for the module advertises 256-bit AES symmetric key encryption capability. Maybe that's the "code" when using a code on the channel. I think talkgroup mode is more secure because you have to create the group in all phones that are to be members of the group. The group ID is a bunch of random digits generated by the app. The group ID is entered manually or the app can generate an ID for you by using the "randomize" feature. I created a talkgroup for our phones by creating the group in the first phone and used the app generate a random ID for the group. Then I created a group in the second phone and manually entered the group ID that was created by the first phone. The app also has an "invite" feature where you can send an invitation to another Sonim DM user so they can easily join the group.
The app has text messaging capabilities and I have used it just enough to verify that it works. I would rather use the app to talk than send text messages. The app has some mapping capabilties too but I haven't tried it yet.
The Sonim DM app takes over assignment of the hardware PTT button. With the phone in airplane mode while using the app, the PTT button stays assigned to the app, regardless of whether the phone screen is locked or unlocked or if the app screen is open or not. The nice thing about this is the phone operates like a simple 2-way radio PTT and you don't have to futz around with the phone and the app to use the PTT. The phone screen can stay locked and it just works like a conventional 2-way radio. It behaves differently if NOT using airplane mode with the app. The app takes over assignment of the PTT button when the app screen is open but other apps may change the assignment if you try to use them. The module and app seems to work best with the phone in airplane mode. This is similar to switching to Direct Talk mode in the old NEXTEL phones.
I haven't done any range testing yet but they are keepers. My wife and I have built like a brick expletive-house ruggedized smartphones with 900MHz Direct Mode capability. If I have to replace a phone someday, it will only be replaced with another Sonim ruggedized smartphone.
