Yesterday, Maps Guide Tom at Google Groups reported to business owners that issues with phone verification have been fixed.
Forum members are not convinced. It seems that issues are still persisting. Business owners who are trying to validate their business are receiving call-backs from Google but there is no voice on the other end and the phone seems "deaf to the keytones."
Even SMS seems to be impacted.
For now, I guess, there's no solution to the problem. We will update this thread if there is a a fix.
Forum discussion continues at Google Groups.