if I understand correctly, you wish to port your cell phone number to your land line telephone, so that your current land line number is changed to your current cell phone, and you can cancel your cell phone service.....
most number porting is done when telephone service is established, so wanting to port a number to a line that has been in service is not the norm, however there should be nothing that would technically prevent this from being possible...
the only thing to be concerned about is that the cell number would need to be able to be ported to the land line... it would need to qualify to be ported (must come from the same area, the cell can not be a diffrent area code, or be a regional toll call from the land line phones calling area)
to begin the porting process you would need to contact the landline carrier, they should take care of everything with taking the number over from the cell phone provider.... do not cancel service to your cell phone until the porting process is complete, or advised to do so by your land line provider... porting can take several days, or in some cases a little more...
you may be required to pay any outstanding balance, or termination fees to your cellular provider before they release the number to be ported.... but your local land line provider should be in touch with you if there are any issues in porting your number that need to be resolved...