Above is the screenshot from http://www.t-mobile.nl/webmms where you can retrieve your MMS pictures. Just provide you telephone number with its given code and its done.
Quoted from Wikipedia:
T-mobile entered the Dutch market by the acquisition of Ben on September 20, 2002. T-Mobile Netherlands, a wholly-owned subsidiary of T-Mobile International, acquired Orange Netherlands from France Télécom for EUR 1.33 billion. This makes it the second largest mobile telephone operator in the country behind KPN.
Ben NL or Ben is a Dutch virtual mobile network operated by T-Mobile NL. It offers voice, text and data service at highly discounted rates. Ben only offers 3 subscription types ranging in price from € 4,95 for 100 minutes/text messages per month to € 14,95 for 500 minutes/text messages per month.
In order to keeps is prices down, Ben has a very limited customer service offering; a Ben subscription can only be purchased online and most customer administration is in the form of online self-service. Also, Ben does not offer subsidies for new handsets. Instead it assumes that its customers will already have a handset.