What approach should I take to export my iPhone contacts to Gmail?
We recommend that you upload them to Google Mail using iTunes.
(PC instructions here.)
Don't forget to make sure they're in the "My Contacts" group, as that's what we'll then sync back down to the phone.
It's a pity that the iPhone won't let you upload them on the initial sync, but at least the iTunes option isn't too painful...
I have personally synced my iPhone contacts (and calendars) with my Gmail account by using the "Exchange server" option from the "Mail, Contacts, Calendars" setting of my iPhone. Generally easy to set up, iPhone contact sync with Gmail is the preferred way for me to export-import iPhone contacts.
Here is a quick summary:
Go to your iPhone Settings and chose "Mail, Contacts, Calendars"
Tap "Add Account..."
Tap "Microsoft Exchange"
Enter your full Gmail address and the rest of your login credentials. Tap Next (top-right)
In the server field type m.google.com and hit Next
From the next slide, turn on Contacts and Mail or Calendars (most important here is contacts)
Optional: If you would like to receive emails on the spot - don't forget to enable Push from your iPhone settings. Otherwise just set your Fetch schedule (under the same Options slide where Push is) to every 15 min or otherwise as desired.
For screenshots and a bit of more detail, see the above article.