Isnumeric

This is my first time when I review code with Isnumeric and trim. can anyone tell me how to interpret or what the following query would return? here is the query

isnumeric(left(ltrim(rtrim(cd.DialedNum)), 1))+ isnumeric(right(left(ltrim(rtrim(cd.DialedNum)), 2), 1))+isnumeric(right(left(ltrim(rtrim(cd.DialedNum)), 3), 1)))

thank you