I agree, great for those running Safaricom's (expansive) per minute billing.
I have installed the app using Wine on Fedora 15 with Gnome 3.0. Notifications on the Title Bar, same place Chrome now puts its controls/title for focussed tab.
recommendations:
add support for decimals in cost per MB.
you can even have field for MBs purchased and Cost so that it automatically calculates this.
Congrats!