The trouble I see with your valuation is what you yourself pointed out, that is it assumes just ADSL. In the end, SWT are forecasting a EBITA of about 1.3 million ( or was it more?) for this financial year. Using your valuation, that would make it a profit of $130 per customer.
I think SWT earn money from other than ADSL. Obviously they have their data storage and corporate services.
I agree with your barriers to entry argument, however SWT have suceeded where other have failed to build up a substantial base of customers and have expanded to all major markets. I don't think its that easy. Look at DFT for example...lot of debt, huge number of shares on issue, no forecast to make profit yet..I don't think it can be that easy.
