Alternative to heroku for facebook PHP apps

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http://serverfault.com – I understand the title is not very suitable for this question.But,I have developed a facebook application in PHP,that will store images of users on server and create a link of that image.Since heroku doesn't allow to store files on their server,i am unable to move those files from /tmp folder to permanent folder.I don't have a credit card so can't signup with Amazon s3 storage to use it with heroku,So i need to know if there is any free trial app engine which also supports storage of files and Have one more question,whats the exact full path of /tmp directory of heroku. (HowTos)