--If you sign up for Ooma Office now, you will immediately see this feature under Settings>System>Call Blocking. Start by ticking the first box Block numbers from Block List and play a busy tone. From there you manually enter phone numbers in the Block List below it. I copy and paste numbers in from our call logs. It shows that you are limited to 1,000 blocked numbers.
--If you have had Ooma Office for some time (we have had it for almost 4 years) you must upgrade your plan to the next highest plan. Grandfathered Ooma Office plans do not have call blocking. I was initially annoyed to hear this but I found out that I would actually save some money on this upgrade.Ooma Office charges $11 per line and then $9 per phone number. I was able to secure $17.95 per line with the new upgraded plan, and that $17.95 includes the $9 phone number cost. You will need to contact customer support and have them upgrade your plan and then turn the call blocking feature on.
--Ooma Office just called me back and had our plan upgraded and the feature turned on. It took less than an hour for all this to be completed. There was no downtime in phone usage.
2 base stations with 2 linx, 5 Yealink T21's