Flexcoin is absolutely going to need a mobile app for it's wallet. I searched on google play and only found mobile wallets for Bitcoin, Litecoin, and Feathercoin. Since I think it would be a lot of work to create a mobile wallet from scratch, that might suggest that we want to branch Litecoin instead of some other coin. I'm don't know all the difficulties of taking one of these wallets and porting them to some other coin like Novacoin, PPcoin or Primecoin, but I'm guessing it's not trivial. I do know that Andreas Schildbach's popular Bitcoin wallet is based on bitcoinj (A Java implementation of a Bitcoin client-only node)
https://code.google.com/p/bitcoinj/ So that could mean in order to create a Primecoin or other non-litecoin based wallet, a port of the client to java is necessary, as that is the native android language. Another question would be do we want to go cross platform, but if so, a lot of these crossplatform alternatives (like PhoneGap) are potentially less secure because they are not compiled. I'm not sure if it makes sense to try to do c++ on android and iOS. I know a little about android development, and nothing about iOS development.
Since most of these coins use the same JSON-RPC interface, it shouldn't be a deciding factor in which coin to clone. It's no more complicated to communicate with a satoshi-type wallet than any other web-service or API.
It's what you have to do with the data that's harder.
Contrary to you, I know nothing about android or iOS dev. But it would be crazy to program any core functionalty of your app into client-side code.
Look to a web wallet with that does feed data (API) to your android app and you can handle the money in a more secure layer of the stack. That way if anyone tries to clone the phone app and do some funky stuff it should just trigger errors at the server side. And you get the added benefit of being able to code your mobile apps in whatever language is handy.
