Telephone Japanese

When I answer the phone at home, what should I say when I pick up? I usually say 'moshi moshi' but my new textbook has this for the caller, not receiver.

Also, what's the best way to say:

"Could I change my appointment from (5pm on Monday 24th) to (Tuesday 25th, around 4pm, if possible)?"

A few variations on the above in order to widen my comm skills would be great, too..

Also, could you show which kanji is used for 'change'? There seem to be a few options.

When you pick up a call, you can say:
- Hai. [Here/call taken here.]
- Hai, [your name] desu.

When calling about changing your appointment, I would start off saying (so that they you know what you are calling about, and start opening up the appointment calendar):
- Yoyaku no henkou wo onegaishimasu. (I would like to have my appointment changed.)
Then they are likely to ask you what your name is, and when your current appointment is, such as:
- O-namae wo mou ichido onegai dekimasu ka. (Can I have your name again?)
- Itsu no yoyaku desu ka. (Appointment at when do you have?)

Then you can say:
- [your name] desu, ima [24-ka no getsuyoubi, gogo 5-ji] ni yoyaku shite imasu ga,
dekitara [25-nichi no kayoubi, gogo 4-ji goro]ni onegai dekimasen ka.
(This is [your name], currently I have an appointment at [5pm on Monday 24th], but if possible, can I come [around 4pm on Monday 25th]?

I usually use the word "henkou," written 変更. This is a change you "make."
If you want to talk about something like the temperatures/season changing, for example, that is "henka," written 変化, something that "happens." Is this what you mean?

AK, that's it exactly. Thanks!

general phone calling,
at first, tell your name, then say what you want to tell.
I think that is better manner.

[zzzzz] san de shouka ? [confirm that you call the correct number.]
(watakushi wa) [xxxxx] to moushimasu. [my name is xxxxx.]
yyyyy san wa oraremasu de shouka ? [May I speak to yyyyy ?]

if the appointment is like restaurant reservations, AK san's way is OK.
however, if the appointment is like business meetings, you should say your name at first.

"moshi moshi" comes from "mousimasu mousimasu", to get the attention of the receiver, perhaps when the phone call connection was still poor and difficult to hear, and it means I want to tell you/talk to you. The receiver would say "hi, xxx desu, or desuga". "hi xxx desuga" means "yes, I am XXX and you are?" If the phone call was paused, dropped or interrupted, you can say "moshi moshi" so now you want to connect again with the caller or the receiver.