Data base structure of a subscriber list
No RDBMS system I know of supports mixing a data-type within a single column. So I think you've got two solutions:


Separate tables - each user's list gets their own Database table. This would allow you the flexibility to customize the data type at the column level.
Flexible data type in the "name" column. You could use a varchar or even a binary blob in the name column and allow the user to store whatever they want in that column. Then, at the application level, you could interpret that data in whatever format you like by, for instance, casting it to an integer.


It sounds to me, since you're hoping to store different types of data with different structures to it, that you should probably just be using separate tables.