But we have
seen snippets of 'pre-destruction Garlemald' in SB and ShB,... and it just looks like Castrum Oriens greatly expanded (same kind of buildings/towers), lots of steel mixed with stonework and cobblestone streets lit by fluroescent light, so very steampunk. Garlemald's capital city somewhat resembles (or resembled)
Vector, the Imperial Capital of the Gestahlian Empire from FFVI - rather fitting too given the use of FFVI magitek armour by Garlemald.
By all accounts there was actually a quiet large technological divide in Garlemald with most of the 'technogadgets' being reserved for the military and the general populace.... missing out (this explains why Cid even today is so lauded by average Garleans as a great engineer, to Nero's chagrin, as he wanted to use technology for
peaceful means for everyone, not weapons solely in the hands of elites, which is why he fled to Eorzea and set up the Garlond Ironworks - it's in the company's motto:
'Freedom Through Technology').
As for radio, we know the Garleans have radio, because
Eorzea uses the exact same technology - it's what linkshells are; advanced radio recievers and transmitters. And we know the Garlean technology is identical because Nero easily hacks into the linkshell feed between Cid and the WoL during the Praetorium with the orb-like device built into his gauntlet, something that would not be possible if it mutually incompatiable. They seem to have certain affinities with mobile phone technology too, especially the phone-like tone in cutscenes whenever a character, usually the WoL, recieved an important call from another NPC.