I know there are apps for WHMCS, but that is all on the administration side.
Only benefit I could see having an app for your clients is for support. But, if they are already on their phone, why not just call?
Not sure I would want to release a billing app. With so many insecure wifi spots, I would be afraid my client(s) would hit one of those when browsing through the app and give away valuable data. Although, I am not all that familiar with security on mobile apps, so that might not be a concern.
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Based of the signatures we receive in tickets many of our clients are already using their blackberry, android or iphone to respond to tickets or billing. I think many hosting companies are looking at the investment vs. the reward which is minimal. If you have a tech savvy group of customers, they know how to use their phone and they are already making the current systems work for them. The application development can cost tens of thousands of dollars and years to get released and approved for the app stores. Everyone's business model is different; however, long run, I think you'll see most hosting related companies stay away from it.
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