My wife and I use Skype to ring 01/02 landline numbers using the £1.50 + vat monthly charge.
We only pay for it using my wife's computer.
We also use both of our computers to speak free online to our friends. (Computer to computer).
We have friends in Gibraltar and ring their landline phone with no problems.
The Skype monthly option should be ok to for your requirements.
Other than the well reported recent problem with Skype nationwide outage, it has been trouble free.