From Forum Nokia Wiki

The MAC address of a WLAN device can be retrieved by the code *#MAC0WLAN# on the standby screen (that's same as *#62209526#).

We can get the MAC address of a S60 WLAN device programmatically as well. This can be done by the following code snippet.

Header:

#include <in_sock.h>

Link against:

LIBRARY insock.lib

Capabilities:

CAPABILITY NONE

RSocketServ socketServ;
User::LeaveIfError(socketServ.Connect());
CleanupClosePushL(socketServ);
 
// Open a socket
RSocket socket;
User::LeaveIfError(socket.Open (socketServ,KAfInet,KSockStream,KProtocolInetTcp));                         
CleanupClosePushL(socket);   
 
// Start enumerating the interfaces
TPckgBuf<TSoInetInterfaceInfo> info;
socket.SetOpt(KSoInetEnumInterfaces, KSolInetIfCtrl);
TBuf<32> macAddr;
 
while(socket.GetOpt(KSoInetNextInterface, KSolInetIfCtrl, info) == KErrNone)
{
    if(info().iName.FindF(_L("Wlan")) == KErrNotFound)
        continue;
 
    macAddr.Zero();
    for(TUint i = sizeof(SSockAddr) ; i < sizeof(SSockAddr) + 6 ; i++)
         if(i < (TUint)info().iHwAddr.Length())
             macAddr.AppendFormat(_L("%02X:"), info().iHwAddr[i] );
 
    if(macAddr.Length()) // remove trailing ':'
        macAddr.Delete(macAddr.Length()-1, 1);            
}
CleanupStack::PopAndDestroy(2);

However, the above MAC address retrieval code works only when your phone is connected to a WLAN. To find out the MAC address even with WLAN turned off, see the below alternative solution (applies to all S60 3rd Edition devices and S60 3rd Edition Feature Pack 1 devices):

This alternatively method uses the Publish & Subscribe keys to retrieve the MAC address when the WLAN is turned off.

WLAN Info API, a part of the Extensions plug-in package for S60 3rd Edition, Feature Pack 1 SDK, contains Publish & Subscribe keys with a MAC address for the WLAN interface.

The wlaninternalpskeys.h header file contains the required Publish & Subscribe category and key information:

const TUid KPSUidWlan = { 0x101f8ec5 };
const TUint KPSWlanMacAddress = 0x00000001;
const RProperty::TType KPSWlanMacAddressType = RProperty::EByteArray;