Would like this feature as well. Showing the network names instead the call letters would be nice.
Odd thing, when I use my computer (chrome browser) to view my.tablotv.com, I see the network names (ABC, NBC, etc…) in the guide. When I view it on my TV (using Kindle Fire TV Stick), I see the local station letters.
On the PC again, on the settings screen it shows the active channels with the network letters. If I click on the Edit Channel Lineup, it shows the local station letters.