I can offer you a Mobile Web Application, that will Sync with Google calendar. It will work on all mobile devices so you won't be limited to just Iphone or Android. Web Applications are relatively new technology, they are like a Hybrid, between Native App and Mobile Website.
Web Apps will become quite popular as people discover how fantastic they are, how much they are like a Native App, without the hefty development cost and much better than a Mobile Website when it comes to efficiency, ease of use. I can supply some examples of previous work I have done. Our Web Apps are hosted on a Web App platform which is supported by Amazon Cloud and all software and mobile phone updates are done automatically from the platform just like Native Apps.
You can list your Web App in the App Store and Google Play if you choose, but it is not necessary as Web Apps open up in any mobile browser and can be saved to desktop so the icon is displayed on the Mobile Screen the same as any other type of App.
They also have active functions like a App, Push to Call, Push to Email, GPS Location finder, QR Code, Share via SMS, Share Via Email. We also link your web app up to Google search engine so if someone is searching for your business website via Google from a mobile device, Google will direct them to your Web App and not your Website.
Please contact me for more information.