Replacing Nulls in ItemTemplate With A String

I have a simple ItemTemplate.  See below.  The data comes from my my SQL database.  My "Cell_Number" field below sometimes is null.  Instead of displaying null, I wish to display some text, such as "Not Available". But, this is not working.  The compiler complains that an expression is expected on my IF statement. Anybody know what is wrong with my IF logic below?

<ItemTemplate>
  <tr>
   <td><font face="Arial, Helvetica, sans-serif" size="1"><%#Eval("First_Name")%></font></td>
   <td><font face="Arial, Helvetica, sans-serif" size="1"><%#Eval("Realtor_ID")%></font></td>


   <% IF (IsDBNull(#Eval("Cell_Number"))) THEN %>
    <td><font face="Arial, Helvetica ...