Wills 1858 – 1919 that are held at the Public Record Office of Northern Ireland have been indexed and that index is available online. The index covers the Armagh, Belfast & Londonderry registries.
Once an entry has been found then the index card gives you full name, date of death, date of grant, estate value, registry where will was proved and an abstract. The abstract is the part that will be of most interest, for example a search for Pottinger came up with a will for Mrs Catherine Casement Pottinger and the abstract gave me this information “Pottinger Catherine Coshnahan of Ballee House Ballymena county Antrim and of St. Patrick’s Hospital St. Edmundsbury Lucan county Dublin widow died 17 October 1927 Administration (with Will) Belfast 18 June to Edith de Burgh Montagu married woman. Effects £1001 5s. 1d.”
However if you find an entry dated somewhere between 1858 – 1900 you can see a scan of the whole will. All at no charge. Wish they would do that for English wills.