Non immigrant o visa (Phuket)

Hi I have just joined.The last few years I have come with Thai wife to visit family..on a non immigrant o visa..I have always gone to Ranong then across to Burma after 90 days.Just looking on Thai Embassy site and they state you can go to immigration office and get extension of up to 1 year after your first 90 days has anyone on here actually done this.??? We all have had experience of the Thai immigration system..lol I would be grateful for any information