I am visiting France later this year. I want my mobile to upload GPS positions online during a whole week.
For that I need a prepaid sim card for France. Google gave me https://www.google.com/search?source=ig&hl=en&rlz=&=&q=prepaid+phones&oq=pre+pa&aq=1s&aqi=g1g-s3g1g-s5&aql=&gs_l=igoogle.3.1.0j0i10l3j0j0i10l5.52481.55992.0.62184.108.40.206.0.0.0.118.599.4j2.6.0…0.0.#hl=en&gs_nf=1&tok=YtYuWo7li1LQMMVG5dduMA&pq=prepaid%20phones&cp=19&gs_id=16&xhr=t&q=prepaid+sim+card+france&pf=p&sclient=psy-ab&oq=prepaid+sim+card+fr&aq=0&aqi=g4&aql=&gs_l=&pbx=1&bav=on.2,or.r_gc.r_pw.r_cp.r_qf.,cf.osb&fp=b10f389bad4889f0&biw=1324&bih=928
From that I got this nice offer from LeFrenchMobile on Euro 7,- for a week: http://www.lefrenchmobile.com/en/data-bundles.html. So that will cover wifi for the mobile.
For Japan Prosa advises hiring a NTT Docomo from Global Advanced Communications. http://www.globaladvancedcomm.com/pocketwifi.html.
Ref: Prosa article: http://www.prosa.dk/aktuelt/nyhed/artikel/mobile-rejsetips-fra-solens-rige/
Next I need the mobile to be charged by an external battery. One such could be like this: http://www.b2c-battery.com.au/accessory_detail.php/24+3974+Universal-External-Battery-for-Digital-Camera,-Mobile-Phone,-PDA,-Camcorder-and-Game-Player. The batteri can be charged in advance with cord to AC.
But even better would be a device where you can just change batteries inside.