If you want to muck about with the registry do so at your own risk: Total Commander is a nice registry editing and file manager tool.
Mobile Explorer Problems
Browsing some web-pages with the built in mobile explorer is borked - Orange tech support in the UK don't know anything about it but the Swiss site has a downloadable patch which fixes the problem.
What does it do?
It changes the "HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Internet Settings\Accept Header" registry key from this:
"application/vnd.wap.wmlc, application/vnd.wap.wbxml, application/vnd.wap.wmlscriptc, application/vnd.wap.multipart.mixed, application/vnd.wap.xhtml+xml, application/xhtml+xml, application/vnd.oma.dd+xml, audio/3gpp, audio/mid, audio/midi, audio/sp-midi, audio/amr, audio/amr-wb, audio/mp3, audio/mp4, audio/MP4-LATM, audio/mpeg, audio/wav, audio/x-wav, audio/x-mp3, audio/x-mpeg, audio/x-mpg, audio/x-ms-wax, audio/x-ms-wma, audio/x-ms-wav, image/bitmap, image/bmp, image/gif, image/jpeg, image/jpg, image/pjpeg, image/png, image/vnd.wap.wbmp, image/wbmp, image/x-bmp, image/x-png, image/x-windows-bmp, message/rfc822, text/css, text/html, text/plain, text/vnd.wap.wml, text/x-ical, text/xml, text/xsl, text/x-vcal, text/vnd.sun.j2me.app-descriptor, application/java, application/java-archive, /vnd.sun.j2me.app-descriptor, video/3gpp, video/avi, video/x-ms-avi, video/mp4, video/x-ms-asf, video/x-ms-asx, video/x-ms-wm, video/x-ms-wmp, video/x-ms-wmv, video/x-ms-wmx, video/x-ms-wvx, */*"
to this:
"*/*, application/vnd.wap.wmlc, application/vnd.wap.wbxml, application/vnd.wap.wmlscriptc, application/vnd.wap.multipart.mixed, application/vnd.wap.xhtml+xml, application/xhtml+xml, application/vnd.oma.dd+xml, audio/3gpp, audio/mid, audio/midi, audio/sp-midi, audio/amr, audio/amr-wb, audio/mp3, audio/mp4, audio/MP4-LATM, audio/mpeg, audio/wav, audio/x-wav, audio/x-mp3, audio/x-mpeg, audio/x-mpg, audio/x-ms-wax, audio/x-ms-wma, audio/x-ms-wav, image/bitmap, image/bmp, image/gif, image/jpeg, image/jpg, image/pjpeg, image/png, image/vnd.wap.wbmp, image/wbmp, image/x-bmp, image/x-png, image/x-windows-bmp, message/rfc822, text/css, text/html, text/plain, text/vnd.wap.wml, text/x-ical, text/xml, text/xsl, text/x-vcal, text/vnd.sun.j2me.app-descriptor, application/java, application/java-archive, /vnd.sun.j2me.app-descriptor, video/3gpp, video/avi, video/x-ms-avi, video/mp4, video/x-ms-asf, video/x-ms-asx, video/x-ms-wm, video/x-ms-wmp, video/x-ms-wmv, video/x-ms-wmx, video/x-ms-wvx"
Note the sneaky move of the */* from the end to the beginning of the registry key. The reason for this is because somehow sites using HTML on Windows IIS Web Servers appear to only read the first 159 characters of the Accept Header Key. I don't know whether its a problem with IIS (cause it ahppens in both version 5 and 6) or with the phone, or the orange network clipping the packet sizes. If anyone does know please contact me.
Low Memory Problems with MMS
If you intend to use MMS and have low memory there's a downloadable patch that fixes this too.
What does it do?
It changes the ""HKLM\Software\ArcSoft\ArcSoft MMS UA\Config\UI\ReservedSpace" registry key from 4096 to 1024.