Using dial plans to restrict overseas calls to land lines

[NeBlackCat]

I'm with PennyTel, who have great flat rates to land lines in various countries. I'm using this to let overseas students studying here call home for 8c or 40c unmetered.

The problem is, though, that I have to stop them dialing overseas numbers which would be far more expensive and metered, like their mates' mobile phones.

I thought PennyTel would have some feature to do that (ie. an "allow flat rate calls only" option) but they don't, and setting up corresponding dial plans in my Billion voip router for all the possible destination countries would be just too big and error prone.

So I wondered whether Voxalot could help, but so far (reading the dial plan tutorial) I haven't found anything.

So my question is: would a "number is landline" test that can be used in dial plans, irrespective of the country being dialed, be a useful and implementable feature?