Is there a way to do SMS from the PC with iOS?
There is currently no way to send SMS from a PC or a Mac.

As you mentioned you can currently send iMessages from a Mac, and you will be able to send both iMessages and SMS from a Mac once OS X Yosemite is released (according to apple.com)

EDIT:

A quick Google search for "send iphone sms from pc" found this: http://www.myphonedesktop.com/