When trying to get a D211 running I detected, that Nokia has mixed up the meaning of the tow operating modes: "Ad-hoc" and "Infrastructure".
In the same WLAN with a defined Access Point on the D211 the operating mode has to be set to "Ad-hoc" while the other clients have to be set to "Infrastructure". Otherwise the D211 will not detect the WLAN.
Why does Nokia mix this up ?
In Nokia D211 User Manual the the two modes are explained in the following way:
Ad hoc: One of the two WLAN operating modes that can be selected when using the Nokia D211. With this configuration option, users can set up a wireless local area network where wireless stations can send and receive data directly with each other without(!) WLAN access points. This type of network is sometimes called a peer-to-peer network. (p.60)
Infrastructure: With this configuration option users can set up a wireless local area network where wireless stations communicate with wired and wireless stations through(!) a WLAN access point. (p.61)
This naming is also used by other manufacturers to these two operating modes. While using access point, Nokia D211 operating mode has to be set to Infrastructure mode.