Buy a GSM phone from AT&T (search DD, there are really cheap ones) or if you have one, have it unlocked and you can buy a sim for $15-$20 that will easily last you your entire stay with plenty of calls, text etc.
Overnight in BKK and 8 hours in Tokyo is sufficient time to get out of the airport if you wish. Depending on what time you arrive/depart there are various things to do.
Haven't stayed at the hotels but for Sydney (and perhaps Melbourne) it may be worth finding someone with Hyatt points and swapping for SPG...
Expensive it will be, especially if the US dollar doesn't pick up...