There was a service outage on Friday and (as far as I could tell using two different 48 accounts/SIMs/phones) another one last night but services seemed to be working fine for me from about noon today. When were you last able to make calls? Is your membership up to date/valid? Are you sure that you haven't used up any call allowances (and thus need an add-on to tide you over to the end of your membership month) or breached the fair usage limits and been barred for the remainder of your current membership month?
If necessary log a support query to get 48 support to look into the problem for you. (I'd post the link but the forum is so slow for me today that I can't spend the time rooting out the links and copying and pasting them - sorry!). Check the "Need Help" forum for the "How to get help" key post.
Hope this helps.
