Avoid "reading notice" to cell phone from Exchange 2007

I have a issue with the notice reads mails sent to cell phones, when sending mail with request for notice of reading, these mails are read from the cellular phone automatically sends the notice reading without asking the user.
I apply the following rules in my MS Exchange 2007 in the transport rules:
 1 - Remove message header Disposition-Notification-To for mail sends from outside my
organization.
 2 - Remove message header Return-Receipt-To for mail sends from outside my
organization.
These rules are applied correctly if you read the mail from the OWA or the Outlook client, but not with cell phones.
I appreciate any help you can give, and I apologize if my English is not very good.