The catch with ISDN is the data call costs. In most cases a ISDN call cost is charged at $0.30 per hour per channel. If your running at the full 128k (2x64k channels) then its $0.60 per hour just for the call costs. Then you have your ISP charges on top of that. Not much of a problem for the light user, but can add up awfully quickly if you accidently leave it on.
However Telstra & BigPond (*shudder*) have a packacge called BigPond ISDN. Which includes the ISDN Home rental (2x64k digital lines) and 128k connection to BigPond with unlimited downloads for $89.90 per month. The added bonus with this is all data call costs to the PigPond dialup number are waived - No internet call costs. To compare that to PSTN you would need to compare 2x PSTN lines, and a dialup account.
2x Homeline Plus = 59.90
1x BigPond unlimited dialup account = 28.95
Total = 88.85 + dialup charges & only 56k connection.
I can maintain 14kB on a 128k ISDN link.
But I'm spoilt at home with a 1536k ADSL link to myself
