I have searched the forums and came across a post by VIG darrenpainter saying the responsibility of creating apps lies with members.
All very well and good but in this world not everybody is trustworthy and eventually somebody will latch on to this feature black hole, and will create an app that will phish peoples credit/debit card numbers or secretly dial premium rate numbers (dialling permissions are used by a lot of 3rd party apps to dial the USSD codes to display balances).
I believe it is the responsibilty of GiffGaff to provide a trustworthy app from which there should be a minimum feature set of:
1) Check Balance
2) Check remaining GB balances
4) Buy GBs
5) Allow administration of auto-topup feature (including auto-goodybag whenever that finally gets implemented)
and possibly (although not essential to anti-fraud efforts):
6) Creation of correct APN settings.
If in-house development is not an option then i believe out-sourcing should be used. If even out-sourcing is unattainable then GiffGaff should at the very least provide endorsement for virus/phishing tested apps that provide the minimum proposed feature set above.
By the number of requests I have seen for something similar it is obvious that this is a very popular idea. I believe out-sourcing may be the best way to go. Using this route a developer could create and design a standardised GUI app for all 4 main OS's (Android, iOS, WP8, BB) in return for endorsement by GG, advertising space on the GG website and they would retain all advertising revenues (app sales revenue if deemed necessary). If an ad-supported app is the way forward then I think most users would be happy with that although I do believe having a paid version that is ad-free is pretty standard these days.
Another thing that could be done is that if the app were to be free it could also include a feature to allow the user to order GG sims if not already logged in to a GG account. This could provide a new and inovative way of recruiting new members.
If the app could create the appropriate APN settings this would surely reduce the number of enquiries about internet settings and enrich the initial experience for new GiffGaffers. I know this can be done with Android (4.0+ rooted or pre 4.0 unrooted) but am unsure of other platforms.
Also the purchase of the BlackBerry Services add-on could be limited to just the BlackBerry app. This could reduce clutter in the user interface and also practically eliminate the chances of users accidentally purchasing the add-on by mistake when they do not have a BlackBerry device.
As the app would enable the user to top-up, I believe it would be essential that any traffic produced by the apps would be tariff free. This is an extension of the tip by rayhoo in which shows how to access the mobile top-up site with a zero balance (Zero Balance Access to Mobile Top-up Site). I would go one step further and say that all access to any top up pages should be free without the need to change settings.
OK got a draft together now of how the app could look (it's basically the website style in HD and on a diet:
A guide to how the app should behave and what should be on which screens is available along with vector images, logos and icons etc. from the following link... Draft for giffgaff App.
EDIT: Edited to include the idea of an ad-free paid version and also the idea of allowing non logged-in users to order a GG sim.
EDIT: Edited to include the idea of creating APN settings and limiting the purchase of the BlackBerry Services add-on to only the BlackBerry app.
EDIT: It's clear that by the time we actually get an official app Windows Phone 8 will be available. As there is a major change in OS architecture it would probably be best to code native to WP8 (WP7 apps will be available for WP8 but only through automated re-coding by Microsoft). It would probably be best to develop for WP8 to ensure future compatibility. For this reason I have changed the 4 main OS's to iOS, Android, WP8 and BB
EDIT: Edited to show draft of how the app could look.