A friend of mine had the C905 (high spec expessive phone) on contract. Had it replaced 4 times dues to faults. Thats not repaired 4 times thats 4 diffrent phones and they all came up with the same fault's. Eventually he had to go to another phone Samsung Tocco ultra I think. I've had a good couple Sony Ericsson phones in the past and have had alot of trouble with them myself but not on the scale my friend did.
Just be careful when buying a Ericsson phone(or any phone really). Do some research on the model you want and see if there are any common complaints. Thats what I always do now before buying a new phone. Good luck with your choice