Can't read email content or send email

I had the same problem on my iphone 4. Was able to correct by following the following iphone support instructions:

Resolution
If Mail does not display message body previews, tap Settings > Mail, Contacts, Calendars > Preview and verify that the Preview setting is not set to None. If it was set to None, tap the number of lines you wish to see, return to Mail, and verify that you now see message body previews.

If Mail is set to preview messages but the previews don't appear, or mail receives blank messages, quit and then reopen Mail* using the following steps:

Click the Home button to suspend the Mail application and return to the Home screen.
Double-click the Home button to view recently used apps.
Select the Mail app by tapping and holding the Mail icon until the red minus appears.
Tap the red minus to quit Mail. This also removes Mail from recently used apps.
Double-click the Home button to return to the Home screen.
Reopen Mail.
* If you are using an iPhone 3G or iPod touch (2nd generation), see this article for instructions on how to force an application to close.

Resolution
If mail receives blank messages, quit and then reopen Mail* using the following steps:

Click the Home button to suspend the Mail application and return to the Home screen.
Double-click the Home button to view recently used apps.
Select the Mail app by tapping and holding the Mail icon until the red minus appears.
Tap the red minus to quit Mail. This also removes Mail from recently used apps.
Double-click the Home button to return to the Home screen.
Reopen Mail.
* If you are using an iPhone 3G or iPod touch (2nd generation), see this article for instructions on how to force an application to close.

does anyone have a solution for this same problem for a iPhone 3G?
The doubleclick-trick doesn't work for this model and I'm getting pretty annoyed by this problem. It's not the first time bur I have no idea what fixed it last time.

I am having the same problem and its just started yesterday

I'm having the same problem - a blank screen. When I hit reply, the keyboard comes up but no text. It's like I'm typing white words on a white screen. Very frustrating!

Thanks!

I had the same issue. The quit mail as described worked for me. Many thanks!!

I had the same problem, I powered off the phone and restarted, it solved the problem.