If you have an iPhone and value security on the road, this is the way to do it. I tried one other app first and it was both buggy and limited. SecuMail is easy to use and integrates well with mail. Support answers questions quickly and competently.
I tested SecuMail by sending messages to a PC with GPG. I was able to en- and decrypt everything thanks to OpenPGP standards. However, I found SecuMail easier to use than the command line on the PC, both for messages and keys.
Great job and worth the money!
Wolfgang P. about SecuMail