I have the same issue on Ubuntu 12.04. Inverse packages cannot be installed since there is a conflict with the smbclient package.

indeed, the smbclient (samba3) package shipped with ubuntu 12.04 explicitly conflicts with samba4-clients. (That is, with the alpha18 package they shipped)

As far as I know, there is nothing we (as packager of a more recent version of samba4-clients) can do about it.
If you really want to install samba4-clients, you'll have to force it with dpkg --force-conflicts.

There is no file level conflict between samba4-client 4.0.1 and smbclient, so I guess it is safe to do so.

Closing this since it is not really fixable.
Unless we maintained a rebuild of smbclient (from samba3) that doesn't have the 'Conflicts' line in its Control file.

Use the workaround mentioned above if you really need smbclient.