This is less in app and more in plugin territory.

MNP, or mobile number portability, is a feature of mobile networks that allows subscribers to take their phone numbers to other providers. Thus, one can not infer from the number itself who the subscriber's provider is.

Maybe you pay different rates depending on your peer's network? Maybe one is just nosy. Either way, it would be great if a software package could query a database (which exists, since such apps exist for iOS and Android, but I'm not familiar with the details) when given a phone number, and return the pertinent network.

What would be even better: hook into Maemo's long-press menus for phone numbers and request the query from there.

Yet better: In contact details, insert a "note" field with the name of the mobile network provider. Cache that info for some reasonable (or configurable) timespan. And add a refresh button.

But I guess that's already pie in the sky territory. In any case, just an app would already be swell