Im in the uk and on O2 and i used this reg edit to make my mms full screen dont no if it will help you but have a go, just back up reg edit first so u cant blame me haha
So, fire up your fav reg editor and browse to:
1. HKLM\Software\Arcsoft\Arcsoft MMS UA\Config\MM1\WspHeader\User-Agent
Change the value of User-Agent to:
"NokiaN95/11.0.026; Series60/3.1 Profile/MIDP-2.0 Configuration/CLDC-1.1" (no quotation marks)
2. HKLM\Software\Arcsoft\Arcsoft MMS UA\Config\MM1\WspHeader\x-wap-profile:
Change the value of x-wap-profile to:
"
http://nds1.nds.nokia.com/uaprof/NN95-1r100.xml" (no quotations marks)
To test, send yourself an MMS : )