It's for people who don't use their phone much, eircom had hidden this scheme away for years so that they could claim they had such a scheme when needed (e.g when they increased line rental charges) but didn't publish any details so people wouldn't apply for it.
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What is a low users scheme?
The main aim of the 'Low Users Scheme' is to limit any increases in the size of telephone bills for all customers who have a relatively low level of usage. The eircom scheme works as follows: if a user spends on average less then €11 a month on calls alone, they can now pay an initial subscription fee of €22.50 (incl. VAT) per month. This will include line rental, local, national, fixed to mobile and international calls up to a value of €5.00 (incl VAT). It should be noted that once a customer exceeds the €5.00 worth of free calls they will pay double on calls up to €6 - €11, after which they will revert to standard call rates.