The idea we have in mind is for "text track", An iPhone app which counts, and keeps track of the amount of SMS messages sent, as this is a flaw in the "native" Apple SMS app design.
The App will start with an empty text box, below which will be a few buttons: COUNT, RESET (as well as simple FORWARD & BACK navigation icons at the top of the screen).
The idea is for the user to Cut & Paste their SMS messages into the App, and tap the COUNT button. This will take the user into screen 2, which shows the total amount of characters used, as well as summaries and running totals.
E.g.,
[text from SMS app appears in box here]
Characters: 178
Words: 53
SMS messages used: 2
Total SMS used to date: 48
Monthly SMS allowance: 600 [this can be changed in a settings menu]
SMS balance: 552
[Reset Totals icon here]
This app is aimed at pay-as-you-go customers who might want to keep track of the SMS messages they send, to solve the problem of over-spending. As you can see, we wouldn't require any advanced graphics, as we want the interface to look as simple and professional as possible. There's already a similar App on iTunes called Word Count, which counts the characters and words but doesn't give any totals for the amount of SMS characters used.
The settings menu would be basic, and wouldn't require anything much other than "click" sounds on cut&paste, the length of each SMS message (but only if this differs from country to country), and a text box/sliding scale of how many texts uses have in their bundle every month.
I have attached some hand-drawn sketches for reference, please forgive their bad quality but hopefully they will allow you to understand my idea!
If there is anything in this message you would like to explain more, please feel free to ask.