Once again, do not confuse clearance to descend ON THE APPROACH -- either after passing the IAF or after intercepting the approach course inside the IAF -- with descent PRIOR TO the approach. There is no inherent "clearance" to descend any further than the explicit ATC cleared altitude when being vectored to the approach course or when cleared direct to the IAF or a fix inside the IAF.
Descent on a STAR or other published arrival route is different, and a clearance may be given to "descend via" the arrival, including altitudes. Clearance procedures and phraseology differs among US, UK, and the rest of the world, though, so make sure you know what your clearance means.
MSA is for emergency and lost communications reference ONLY.