Very nice comparison of Mailchimp and Aweber. It looks like both Aweber and Mailchimp will suspend you without notice for seemingly trivial reasons. I think it is always good to have a backup system of your own. I use autoresponderplus and 12all scripts and have backups of my campaigns. Aweber is a great service you just never no when you might offend them. It seems like Mailchimp is even touchier. I think the best solution is not to rely completely on any one service. Nice post!
MailChimp does not allow content that references the terms “make money at home”, ‘get rich quick’, or other similar terms. These keywords overlap keywords used by ISPs and SpamCop organizations to block content associated with spammers from those industries. This generates too much risk for us to encounter automated spam filter blocks for all of our customers.
The Autoresponder 2.0 is probably the most advanced feature that GetResponse launched a couple of months ago. With their new autoresponder feature we can now create message cycles that are timely and relevant — all adjusted precisely to subscriber needs and expectations and send them automatically. As a result the open and click are higher and hence lead to more conversions. - Ram Shengale
I am not signing up for an account so I don't know exactly how the API works, but if I were setting up an iPhone App to work with this, I would use the rails plugin. Rails gives you JSON communication for free (IE no extra work required) http://guides.rubyonrails.org/layouts_and_rendering.html see section 2.2.9. Then use on IOS app use something like: http://code.google.com/p/json-framework/ to interact with that.
Think about implementing referral links to incentivize your subscribers to spread awareness about your brand, too. Referral links allow your current customers to promote trackable links for your business. In exchange for sending new paying customers your way, you can give them incentives like discounts, coupons, vouchers, cash, prizes or redeemable points.