If you flash the latest version of LineageOS 14.1 with Android 7.1 onto a Samsung Galaxy S5 the cellular voice service works as does SMS, but I found that MMS and cellular data do not work. This is because Tello is a MVNO using Sprints network. The default Sprint network settings in LineageOS are not correct. I will briefly explain how to fix them here.
We will be changing the APN settings on the phone. APN stands for Access Point Network. These are important configuration items for your phone to properly connect to the cellular network and will vary by provider.
To reach the APN settings menu on Android with LineageOS 14.1 nagivate to Settings->Wireless & Networks->More->Cellular Networks->Access Point Names.
At this point you can edit or add new APN configurations. LineageOS comes with several standard providers pre-configured, but Tello is not one of them so we will add a new APN by selecting the plus button at the top of the Access Point Names menu.
Name = Tello
APN = n.mi.ispsn
Proxy = Not set
Port = Not set
Username = firstname.lastname@example.org
Password = Not set
Server = Not set
MMSC = http://mms.sprintpcs.com
MMS proxy = 184.108.40.206
MMS port = 80
MCC = 310
MNC = 120
Authentication type = Not set
APN type = default,mms
APN protocol = IPv4
APN roaming protocol = IPv4
Bearer = LTE
MVNO type = None
MVNO value = Not set
Save this configuration and your data and MMS should now work.
Here is some additional information on the meaning of each APN settings above
Another description of APN settings is available here: Details of APN settings