For those who wish to spot or check spots from a German Summit, it should be noted that all three cell networks in Germany (Telekom(T-Mobile), Vodafone and Telefonica(O2)) stopped their 3G data services on June 30th. The existing frequencies and mast space are to be re-used in the expansion of the 5G networks into regional areas.
Even if (like me) you have a 4G/LTE smartphone, this may not solve the problem as many such (older 4G) phones have the 1800/2100 MHz LTE bands but not the 850MHz band that is used in regional Germany (and across many regional areas of European countries including the UK). This is the old CDMA frequency and is known as “Band 20” that has been re-purposed for 4G. In large cities the 1800/2100 MHz bands give good 4G coverage but when out on a summit (as I was on Monday) it is hit and miss if you can find a cell tower with one of these bands and hence have data capabilities to your phone.
In theory some data connection might be possible via the old 2G network, which is still in place however for current Apps that is far too slow. I also found I was unable to send SMS texts on Monday, which I thought should still be possible.
If your phone has Band 20 4gLTE support, you should have coverage over most of Germany but if visiting with a 3G only or early 4G without B20 you will be lucky to get a data connection once you move into the countryside.