I now have a cellphone plan, where all outgoing calls are metered and very expensive, except for unlimited calls to 3 favorite numbers, which are included in the plan. For our international calling, we are already using a discount carrier activated through a dial prefix, which also supports a local land-line dial-in access to be usable from mobile phones. By declaring the access number as one of my favorites, I can make unlimited calls from my mobile phone at the substantially lower rate of the discount carrier. The only problems is that making calls through the indirection of a voice-prompt menu is very cumbersome!
This is where Phonecard Express comes in. This highly customizeable application inserts itself almost transparently as a filter between the Android system dialer and the telephony subsystem. Whether a call is made from the dialer, the address book or any other intent, the call setup is intercepted and potentially routed through a calling card service. In addition to supporting multiple cards and their specific call setup sequences (access numbers, voice prompt, PIN, etc) Phonecard Express also supports various policies which control which calls are routed through which calling card account or dialed directly. For people who travel internationally and tend to store all numbers in the address book in the GSM style "+" notation, Phonecard Express supports logic to expand the number with a configured international call prefix prefix.
In my setup, I have exception rules for my other two favorite numbers as well as the voicemail access to use direct dialing. For all other cards, the call is automatically routed through discount carrier account. The integration is so seamless and transparent that it is almost scary and the only noticeable drawback over the standard call flow is the noticeable larger post dial delay, partially from loading another application during the call setup flow and from having to dial an access number and key in the number as DMT signals on AVS prompt before the call is really initiated. On the other hand, this is a small price to pay for saving an order of magnitude in per minute calling cost.
Phonecard Express is a great example for the flexibility of the Android platform, where 3rd party applications can very deeply integrated and partially replace default system functionality.