AppEngine GqlQuery (WHERE NOT)

I want to find all employees from a company where the telephone number is NOT empty.

Now I have this:

db.GqlQuery('SELECT * FROM Employee '
       'WHERE company = :company '
       'AND phone > :nophone', company=company, nophone=None)

But this always prints out empty results although there are items with telephone number.

try to use

db.GqlQuery('SELECT * FROM Employee  '
  'WHERE company = :company '
  'AND phone != :nophone', company=company, nophone=None)

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