[mschuster91]

They did, at least O2 had a inland roaming with Telekom back in its early days; after the merge between O2 and EPlus the networks are still doing inland roaming afaik.

And I'd say with O2 you don't get anywhere next to 90% LTE - not in the countryside (where Vodafone and Telekom often enough also offer EDGE at best), but also in major cities. Berlin is the worst (at Hbf and Gesundbrunnen you're lucky to have actually working HSDPA!), next comes Hamburg and Duesseldorf. Munich is fairly good, also in the subways.

The general problem with O2 is when the network gets congested - e.g. demonstrations, festivals, sometimes on Autobahns even traffic jams! - there is no Internet service at all. The phone may show a "4G" indicator but no traffic goes through. Telekom and Vodafone seem to handle sudden congestions way better, I am not sure how though.

[germanier]

Sorry, I edited my comment while you replied. O2 officially is at 80% LTE coverage according to the latest BNetzA report. But as far as I know they often use cells that can't handle the needed capacity.

When the networks where new, some offered roaming in some areas, I remember that as well. The E-Plus/O2 roaming was more of a technical thing when they merged, it should now be largely gone and a single network.

[mschuster91]

It's iirc their backhaul network that can't keep up, not the technology they use in their BTS. Telekom and Vodafone have large fiber networks (Telekom for DSL, Vodafone for cable-Internet) so they can use existing infrastructure (conduits, electricity lines, right-of-way for houses housing concentrators, routers etc) while O2/Eplus had to build out/rent everything.

In addition O2/Eplus historically got the cheaper but more inefficient frequency ranges which made them the "low cost" players.