Character Limit is the number of characters you can display in a USSD Menu. This depends on the Telco.
Safaricom KE : 160 characters.
Airtel KE : 184 characters.
For both Telcos if the menu is long they automatically break up the menu and adds the '98:More 00:Back' section etc ( this is sometimes referred to as automatic pagination)
The maximum number of characters expected in the user input(that is what the customer may enter in response to your menu) is
Safaricom KE : 80 characters
Airtel KE : 90 characters
For any further clarifications send an email to firstname.lastname@example.org