Reporting error code 206602 on the Nintendo support site results in an interesting message:
Error Code: 206602 Nintendo DSi Shop – Nintendo Points Card or Nintendo DSi Download Ticket Error
There appears to be a problem using the Nintendo Points Card or a Nintendo DSi Shop Download Ticket.
* Make sure you entering the number in the correct field in the Nintendo DSi Shop.
o For Nintendo Points Card redemption, enter the number off the Nintendo Points Card in the "Add Nintendo DSi Points" section off of the main Nintendo DSi Shop page, and select "Redeem Nintendo Points Card."
o To redeem a Nintendo DSi Download Ticket number, such as for the Nintendo DSi Speak Channel, enter the number off the Nintendo DSi Download Ticket in "Settings and Features" off of the main Nintendo DSi Shop page, then select "Nintendo DSi Download Ticket."
* After verifying you are entering the number in the correct location, retry the number again and make sure it is being entered correctly.
Voice chat via DSi confirmed?