Hello,
I'm trying to send an MMS to a nokia 6600, but it sends always a deferred notifyresponse instead of downloading the message. The "On receiving msg" option is set to "Retr. immediately".
The notification PDU is:
429496718042949671704294967192484848484848484848484848484853480429496718142949671844294967177224294967168575449514956485255524784898069618076777804294967190109109115324049410429496717842949671684294967182230429496726942949671765429496716931814294967168429496717110411611611258474710910911547631051006153480

I faced the same problem on Nokia 9300.