I use my Gmail account to sync my contacts and calender but do not use it for mail. In my mail accounts on the phone I have 3 accounts set up, none of them gmail, and they are all set up correctly.
What I did was I went into contacts and selected send an email to my friend and which ever program popped up by default was the one I used. Now for some reason when it sends email to my friends iPhone it shows up as being from
myusername@gmail.com and not the default email account
myusername@sbcglobal.net (I set this as the default in the settings option) this only seems to be a problem with his iPhone and not other email as I can send myself emails to all 3 of my accounts and they come from my default email.
So what I did was go into menu/settings/data sync/Google and turned off Gmail as I think having the sync enabled maybe causing the problems. We'll see if that works.
For the life of me I cannot find why his iPhone can not send email to Gmail accounts. In the Apple forums there are a lot of posts with issues with setting up and using Gmail accounts on an iPhone, something to do with POP and IMAP issues within Gmail itself, but nothing about my friends specific problem.
And I have to say this after setting up 3 iPhones at work for my bosses. They suck a**!! I love my Eris and its is so much nicer as opposed to the iPhone.