These fields are pretty easy to convert during an upgrade.
1) Create a new user custom field. If it's not possible to replicate the full functionality using a text field type (eg note that Skype can show an online/offline icon) then you will have to create a special new user profile field type as a new plugin.
2) Copy existing data into this new field.
3) Drop old column from the user table.
4) Make sure that all code no longer relies on this field.
5) Make sure that all code that provides user data (eg web services) behaves as expected and APIs are not changed.
- Web URL