I have a 2006 VITO LWB 109 CDI (W639) without the multi function steering wheel and has the 'M' and 'R' buttons on the left hand side of the speedo cluster.
After a little searching online I have today managed to reset the service indicator using the following steps :
1. Insert Key and turn ignition on to position 2 (ie. 2 clicks). All the usual lights will illuminate.
2. Then press button 'M' twice (This must be done as soon as the ignition is switched on) and the service display will show (either 1 or 2 spanners/mileage will show).
3. Now turn back the key to position 1, press and continue to hold the 'M' button and at the same time then turn back the ignition to position 2. Keep holding down the 'M' button until you hear a long 'beep' sound (around 10 seconds) which will tell you the service indicator has been reset. The new mileage indicator together with either spanner 1 or 2 will show displaying the new mileage to your next service.
4. Release button 'M'.
Job done !
You can repeat the above steps to switch from Spanner 1 or 2 for your next service depending on which service you have just carried out.