The Zello Android app supports screenless network radios like the Inrico T199 shown below. TYT W700 network radios can also be configured using the same steps as the Inrico T199.  

The steps below outline setting up and configuring Zello for the Inrico T199.

Installing the Zello app and configuring an account

Since the device doesn't have a screen, you'll need to use a computer to configure it.

1. Download an Android remote control application to your computer. For example, Vysor is one such app that works on both Mac and Windows PCs. NOTE: Zello is not affiliated with, or endorsing, Vysor
2. Connect the Inrico T199 to your computer using a USB cable 
3. Use Vysor to configure the device and install Zello from Google Play or the Zello website.  

Creating channels and contacts for the selector knob

Up to 16 channels and/or contacts can be mapped on these devices. For assistance setting up your device's selector knob, see this article. 

It's helpful to name your channels and contacts by adding a two-digit numercial prefix indicating it's position on the knob before you begin mapping to the radio. As an example, "01 Station HQ" would be the first knob selection, while "02 EMS" would be the second knob selection. You will need to use these names during the mapping task below.
Network admins: Use the Management Console to create channels and contact usernames with the same two-digit prefix naming convention as the free app.

Mapping the push-to-talk button and secondary buttons

1. In the Zello app, go to Menu>Options>Push-to-talk buttons
2. Click the "+" icon, then press the PTT button on the side of the device. The Zello PTT button will be added to the list
3. Repeat for additional buttons
4. For each button added to the list, you can edit button details and select a specific channel or contact to key up with when the button is pressed. This is especially useful for secondary buttons. For example, you can have secondary buttons mapped to an emergency channel or contact so they are always accessible.

Mapping Zello channels and contacts to the Inrico channel knob

The Inrico T199 radio includes a knob that allows you to switch through channels. To map Zello channels to channel numbers on the T199, it is important that channels must be named correctly from the beginning, because Zello Work users are not able to rename users and channels.

Given everything is already named correctly, here is how it will work:

1. Select Channels and then click on the channel that you want to verify that is mapped. The talk screen for this channel will display. Your channel should already have a two-digit prefix in its name to indicator knob position. For example, you might have a channel named "13 CB Friends" so it will be mapped to knob position 13. For channels with numbers under 10 a leading zero (i.e. "01", "02" etc) is used. There can be mapped up to 16 channels and contacts combined total.
2. Exit the channel talk screen and then rotate the knob to test. When the channel is selected, its name will be announced using text-to-speech. The channels are switched in their numerical order. For example if you have channels 01, 07 and 13 assigned, rotating the knob will make channels switch in the following order: 01 -> 07 -> 13 -> 01 -> 07, etc.
3. For verifying that selecting contacts works, instead of selecting Channels in step 1, you would select Contacts that you want to map. Be careful that unique prefixes are used for different channels and contacts. 

Note: The network admin can choose whether the knob refers to indexed (numbered) channels or contacts by toggling the setting in web console (Settings -> Android Hardware knob mode)