This information was obtained through requests submitted by Scott Cobb under the Texas Public Information Act.
12,201 people wrote Perry opposing the execution of Frances Newton last Sept. Ten people wrote him supporting the execution. Most recently, 2,627 people wrote opposing the execution of Jaime Elizalde on Jan 31. Nobody wrote Perry supporting Elizalde's execution. For the execution of Marion Dudley on Jan 25, only 141 people communicated their opposition to the execution to Perry's office and nobody wrote Perry supporting the execution.
Here is a pdf of all the information, broken down into communications from inside Texas, other U.S. states and outside the U.S and including both written correspondence and phone calls.
Below is the same information posted on one of those new web 2.0 spreadsheet sites called Num Sum.