help want phone that can instant mess aol aim

From Uk,

hi im after a phone where i can use aol aim on it to chat.ive never owned a contract phone as prerefe pay as u go but im not sure if i can get a phone that does this on pay as u go?.ive been told about the sidekick 3 from tmobile but unsure where to get it and is it only on contract and if so will the aim b unlimited with the monthly line rental or will i be charged by the min etc.as i say id really prefere a phone that does this on pay as u go but dont know how it will work etc or if any such phone exsists please help if u can .cheers