Trying the example (from the ZK demo):
<zk>
<listbox id="box" multiple="true" checkmark="true">
<listhead>
<listheader label="Name" />
<listheader label="Gender" />
<listheader label="Age" />
</listhead>
<listitem>
<listcell label="Mary" />
<listcell label="FEMALE" />
<listcell label="18" />
</listitem>
<listitem>
<listcell label="John" />
<listcell label="MALE" />
<listcell label="20" />
</listitem>
<listitem>
<listcell label="Jane" />
<listcell label="FEMALE" />
<listcell label="32" />
</listitem>
<listitem>
<listcell label="Henry" />
<listcell label="MALE" />
<listcell label="29" />
</listitem>
<listitem>
<listcell label="Mark" />
<listcell label="MALE" />
<listcell label="15" />
</listitem>
<listitem>
<listcell label="Jeffery" />
<listcell label="MALE" />
<listcell label="17" />
</listitem>
<listitem>
<listcell label="Rebecca" />
<listcell label="FEMALE" />
<listcell label="21" />
</listitem>
</listbox>
</zk>

with ZK 6.5.0 on Motorola Atrix (Android 2.3.4), checkboxes are not selectable.