First you will need to export them to your computer.
In webtext on o2.ie click "contacts and groups" and then select all the contacts and in excel click paste special and paste as text. The same works if I click "more actions" "Print (overview)" and then click paste special in excel and click paste text. I'm using office 2010 but I can confirm it works in excel 2007. From there you can organise the phone number column by right clicking on the column and clicking format cells. Choose number from the category under the number tab and choose 0 decimal places. Then you should be able to see the list of names and numbers. Save the file as tab delimited (text) or comma delimited (csv) format and it should be importable into most software programs.