I downloaded the 21 px font to my Pixi Plus and I don't see any difference in the messaging font. Are there apps that interfere with it working properly? I have the following patches installed:

100 more autoreplace words
21px fit
Add option to send link message
Add space between snooze
Additional contact labels
Advanced configuration for app launch
Alarm daily options
Batter icon as percent
Bookmarks list button
Charging alert vibrate only
Close on hangup
Create birthday events
Default to month view
Device menu ultramix
Enable dialpad vibration
Enable landscape email
Enable landscape messaging
Enable landscape youtube
Enable vibration
Faster card animations hyper
Just charge by default
Match state to area code
More reminder alarm times
New task auto details
No autodial from call log
Read/delete all email
Slider answers to speaker
System menu initial framework
System menu mode menu
Timestamps clean