[Motel75]

All right, I'll start this off.

In Germany, GSM 900 service (the "D network") began in 1992. The original prefixes were:

0171 for "D1" (then Deutsche Bundespost Telekom, ie the government. Now T-Mobile, but still often known by this name)
0172 for "D2 privat" (now Vodafone, then a consortium led by Mannesmann.)

The "E network" (GSM 1800) providers came later:

0177 for E-Plus, from 1994
0179 for Viag Interkom (now O2), from 1998

New prefixes began to be assigned in 1999 to increase capacity (the first were 0174 for Vodafone and 0170 for T-Mobile). Of all these, 0171 and 0172 are now the least common (you are extremely unlikely to find a prepaid number with them), and 0172 is considerably rarer than 0171. Newer prefixes use eight-digit numbers; these use seven.

There are two old prefixes that are not available:

0161 for the old analog "C network" (1985-2000). These users were migrated to T-Mobile, but were given new numbers with a different prefix.
0150 for Quam, a short-lived MVNO (2001-2002) that was planned as a future UMTS operator. Customers were not given the option of keeping their number when it closed.