Will not record, playback is just pixels - Panasonic NV-GS400 Camcorder

Sounds like dirty heads.
A clean and adjust of the tape path will most likely sort it out.

Yes, mp4 is supported by nokia 7230

http://europe.nokia.com/find-products/devices/nokia-7230/specifications

Video codecs & formats

• Video capture at up to 320 x 240 pixels (QVGA) at 15 fps
• Video recording file formats: MP4 (default), 3GP (for MMS); codecs: H.263, MPEG-4
• Audio recording file formats: AMR-NB
• Video playback file formats: MP4, 3GP; codecs H.263, H.264
• DRM support: OMA DRM 2 video, Windows DRM-10, WMV

Most important is to get information from your service provider to confirm if the network supports streaming video. The phone by itself supports all the following streams as you can download and watch on this Android phone.
The supported features/tech specs are as follows;

Audio codec
MP3, AMR, AAC, AAC+, WAV, WMA
Video codec
(Video Recording / Video Playback)
Recording: MPEG4 @VGA15fps
Playback: MPEG4, H263@VGA30fps, WMV, DivX, Xvid
Main Camera
3Mega pixels AF

I just made contact with a service tech who seems very competent and who won me over. Have problem with video and audio dropout similiar to dirty heads on a 10 year old DCR-VX2000 but which is a larger problem attributed to worn parts which will need replacement. Do not know how old your unit is, but will share name of person/company if you wish. Only thing that worries me is if you by chance had had yours repaired by them!!! They are a Southern California company.

Check your signal strength on your second tuner. Dont forget to check all satellites and, if you use the signal meter instead of system test, a few odd and a few even transponders.

It sounds like it may be low.

i think it needs a cleaner

Never use tape head cleaners, I suggest just use new blank tape and I recommend TDK minidv tapes, new tapes already serves as video head cleaner. If the problem is still there, manual cleaning is needed or it is possible that your video head is worn out already, you need profix then.

pixelation on the right side is an indication of misalignment of the exit roller.  don't try to align it yourself unless you're experienced in this repair.

a simply cleaning of video head will solve the problem. if the head clean cassette is not working try doing manualy or get it done by some expert.

Some possible cause of lines, noise or pixelation during playback are: 1. Dirty heads on the recording machine. If the heads were dirty at the time of recording, the dirty heads didn't record a strong enough signal on the tape. The damage is done for this tape and recovery is unlikely. Best advice here is to use only premium grade new tapes and keep your camcorder clean by occasionally running a cleaning tape. 2. Physical tape damage. Any distortion of the tape will result in mistracking and subsequent loss of data. 3. Built up oxide deposits or other debris in the guidepost corners can also result in tape edge damage. Keep your machine clean! 4. Improper tape storage - Even short term exposure to high temperatures over 130 deg f. can permanently damage the tape. The black cassette housing readily absorbs the sun's infrared rays and internal cassette temperatures can soar even if left in direct sunlight on just a warm day. It doesn't take much heat to slightly distort the plastic shell or ruin the tape contained within. * Try other tapes to ensure the problem lies within the tape and not the camcorder. * If the problem becomes apparent on all tapes, try a head cleaner. After cleaning the heads, the tapes may not play cleaner if the recording was done while the heads were dirty.