The first few lines are from the script of A Study in Pink. I don't own them, or the characters.
Sherlock smirked. "You've got a psychosomatic limp, of course you've got a therapist. Then there's your brother. Your phone. It's expensive, e-mail enabled, MP3 player. You're looking for a flatshare. You wouldn't waste money on this - it's a gift, then. Scratches. Not one, many over 's been in the same pocket as keys and coins. The man sitting next to me wouldn't treat your one luxury item like this. So it's had a previous owner. Next bit's easy. You know it already.
'Harry Watson - from Clara xxx'."
John asked, "The engraving?"
"Harry Watson - clearly a family member who's given you his old phone. Not your father - this is a young man's gadget. Could be a cousin, but you're a war hero who can't find a place to live. Unlikely you've got an extended family, certainly not one you're close to, so brother it is. Now, Clara - who's Clara? Three kisses says romantic attachment. Expensive phone says wife, not girlfriend. Must've given it to him recently - this model's only six months old. Marriage in trouble, then - six months on, and already he's giving it away? If she'd left him, he would've kept it. People do, sentiment. But no, he wanted rid of it - he left her. He gave the phone to you, that says he wants you to stay in touch. You're looking for cheap accommodation and you're not going to your brother for help? That says you've got problems with him. Maybe you liked his wife, maybe you don't like his drinking."
"How can you possibly know about the drinking?" John asked, slightly nettled.
Sherlock rolled his eyes. "Shot in the dark. Good one, though. Power connection - tiny little scuff marks round the edge. Every night he goes to plug it in and charge but his hands are shaking. You never see those marks on a sober man's phone, never seen a drunk's without them. There you go, you see? You were right."
"I was right? Right about what?"
Sherlock smirked again. "The police don't consult amateurs."
John smiled. "That was amazing."
Sherlock smiled back, hesitantly. A true smile, a shy smile. "You think so?"
"Of course it was. It was extraordinary. It was quite extraordinary. You are very clever."
"I know."
John hesitated, then plunged ahead. "Except…you were dead wrong."
"What?! No. You're just trying to get a rise out of me like the others!" Sherlock yelled.
"Nope. 'Fraid not," John said sadly.
"But, the scratches, the new phone, and the inscription. I know I was right!"
"Harry was my grandfather. He worked as an electrician before becoming an engineer late in life. He worked on this phone's previous models, but his Parkinson's got the worst of him. Grandmother Clara bought it for him as a gift. You were right about one thing- Grandmother died last month. Grandfather is in a home now. Saw no use for his phone there, so he gave it to me."
"No no no!" Sherlock was pouting.
John ignored his temper tantrum in favor of looking out the window. "Oh, are we here? Where exactly is here?"
Sherlock, in turn, ignored John and stalked angrily away.
John turned to see his new flatmate stomping childishly towards a crime scene. "Sherlock? Sherlock?! Sherlock!"
For those of you who don't know, Parkinson's is a disease where the afflicted gets very shaky, among other symptoms. When the disease progresses enough, the patient may lose the ability to dress themselves, feed themselves, or perform other activities of daily living- such as plugging in a phone smoothly.