Here are some interesting stats from Vodafone they have published earlier this year on the number of base stations they have in Germany. In the press release they mention that they have more than 20.000 GSM base station covering 99% of the population and 13.000 UMTS base stations covering 80% of the population.
Taking into account their current customer base (or more precise the number of SIM ards) of around 34 million let’s do some maths with the numbers:
For GSM: 34 million customers divided by 20.000 base stations means that each base station on average serves around 1700 customers. Most base stations have three sectors, so each sector covers on average 1700 / 3 = 566 customers.
Number of voice minutes on average per user per month: 111 minutes. So each sector of a base station would on average serve 111 minutes per month * 566 customers = 62900 voice minutes. To count in effects such as busy hour, let’s say those minutes are handled in 15 hours (a gross simplification…) of the day. 62900 / 30 days / 15 hours = 139 voice minutes per sector per hour. Given that most sectors are equipped with 2-3 Transceivers which can each serve between 6 and 8 voice calls would result in more than enough average capacity and still leave ample room for GPRS/EDGE services. Actually, I think the number looks rather low compared to what should be possible. Not sure why that is...
Note that in big cities, the base stations are probably much higher loaded due to the higher population density. That’s easily missed when working with averages.
Concerning the UMTS numbers, it’s a bit difficult to make meaningful similar calculations here. Vodafone says they have 5+ million UMTS customers. That probably means they have that many customers with a 3G phone. However, it says nothing about how many people have locked their phone to 2G for various reasons and also gives no indication on how many people use data intensive 3G Internet access. So I'll leave those numbers as they are for the moment.