My friend is using her iphone only for imessages. She is using her email address as her contact name. So when I send her a message I type in her email address. Whenever I send her a message using a device other than my iphone and I type in her email address will she still get it on her iphone or will it only go to her email account?
iMessage is a service from Apple which works from iOS devices and Macs with OS X 10.8 and later only and is using the device's data connection rather than the regular phone connection.
Using the e-mail address with another device's text messaging system will most-likely result into an error telling you that the e-mail address entered is an invalid phone number.
Sending a message with ANY device as regular e-mail will result into your friend receiving the message as e-mail instead of an iMessage.