This is a problem on older celicas, I know as I just bought a 2001 celica with an Fubar engine ( I knew it was fubar btw!)
Toyota will change the block, pistons, rings and oil pickup pipe under warranty, however the car I bought was just out of warranty and the guy had missed a service. Bad luck for him, cheap Celica for me!
Fortunately my old man works for Toyota so parts @ trade price, no labour costs and I get a brand new motor
When this problem occurs, they burn oil at an unbelieveable rate, so even the most conscientious oil checking will probably miss it.. and by the time the oil light comes on, the damage is usually done. Hope the damn light works better on my motor now!!