This also won't help with coverage, of course, and if you want a phone number, you would need an extra SIM for that.
It's not very cheap if you want to use it for months, but plenty of other options around too
Amusingly this plan includes 40Gb/month in Germany at no additional costs which is much cheaper than a German plan.
My “solution” for a while was a stack of prepaid throwaway SIM cards with unlimited data from a nearby country and a cheap USB powered 4G hotspot in my bag powered by a power bank. They would last about a month.
I’ve also seen some cheaper providers than this in DE but they limit 5G to 50mbps :(
You can do the trick of buying up a stack of prepaid SIM cards when travelling and using a cheap dongle, but it’s a lot of effort and eventually stops working - probably due to the IMEI being banned though I’ve not confirmed that.
It’s less effort to just snag a new local SIM upon landing at most airports and using it as a hotspot.
Or, you know. Rolling out WiFi as a public service. Which would be kinda cool.