buddy, to transfer the sis files or any other file to another phone, first u need to change the extension of that file using any file explorer and transfer.
for example if you want to transfer aaa.sis then delete .sis and rename it to any other and transfer.
another method is by installing zipman. With this you make a zip archive of the files u want to transfer and then transfer that zip archive file. Note that the file will be in zip compressed format and the recieving mobile should also have installed zipman or zip software.
Hope this will help you.