yes, use ssl whenever you want or need privacy, especially in wireless networks. There are many duping techniques to capture your data in wireless networks. However, if your data is 'scrambled' via ssl encryption, the captured data will take many many years to unscramble without the proper authorization.
If you cannot access your web based email through your cell phone, but sure you have the proper login information. But ssl should work out of the box for iphone.
What if there is an data breach after I certified my website with SSL?
How do I find my current ssl?