My input is dont worry about what you were proving what you were talking about ie the content of sms, im's. Lets be honest they know they could be faked and most will have names other than your legal name and even then anyone can claim joe.bloggs@yahoo.
But you could show the constant communcation via sms either from print outs on a phone pc suite or via a bill if you have a phone on a contract.
Personally i would consider proving the constant contact more and physical meetings back in 2005 one of the few tick boxs (of things the adminstrator had to find evidence of in your submitted paperwork) that was on a scarp of paper was photos together..
No one is likely to hand over recordings of phone calls to an ECO and personally i dont see what ECO is going to read though chat logs. But showing that your two usernames would regulalry chat (also mentioned i think in the computer section) just as you might show your phone call records.
Proof of financial support, phones, passports with stamps, receipts from trips together, proof of constant communication, proof you can support your mahal in the uk, proof of a place to live in the UK which is suitable, and finally proof its a geniune relationship.
