Under the Labels tab change the Method from Label all the features the same way to Define classes of features and label each class differently.
Click on the SQL Query. In the Select Box just add "Name" IS NOT NULL and click OK (you can rename this from Default by choosing Rename). Make the Label Field = Name
Then click Add (to add a new class). Name it. Click the SQL Query and in the Select Box just add "Name" IS NULL and click OK. Make the Label Field = Number.
That should do the trick.