How do I bypass the call for service message on my Toshiba 2500c

SOURCE: toshiba 2500c Fax board

No need, just the fax board in order to do faxing. But if u have printer kit, u can do network fax.

SOURCE: Toshiba eStudio 2500c - CA00

This is a pretty complicated issue/problem. there are 5 pages devoted to this issue in the service manual. This issue would be best handled by a technician. but you could try the following....
[CA00] Color registration abnormality
<Color toner low density>
Turn on the copier holding down 0 and 8 and wait till it boots up into its service mode..then enter code 2692 “Prevention of color toner low density / change the zero to 1.
Then change code 2693 “Prevention of color toner low density / Judged number of sheets setting” value to 40 (default 20).
Make sure you have cleaned the main charge units by fully extending the rods with the green handles for each color.(open the front door) and use the plastic wand attached to the front door to clean the laser glass for each color..there is a small **** under each color unit to slid the wand into..felt side down on the wand.

Like I said there are several other complicated ways of fixing this.