my other 02 account

i have a d900 in the uk . my other o2 account ran out as of end may . o2 offered my missus a u 600 gave her the letter so she could vouch for me .she did have a d500 cast off from me` nice phone` ...same tariff less than 20 quid . well cheap .is her phone better than mine . if so gutted , although she said can swap .as she is lloverlyyy.what has the u got that the d aint.any links.i think i will always go for a d from samsung . PLZ PUT fm on it .