Since your dad uses the internet almost every day, I think he just needs a few web links for the best call-by-call rates.
All of the following links work correctly in a "wap-capable" browser like Opera.
(These links do not work with Firefox or Internet Explorer.)
UK:
http://wap.teltarif.de/db/res.wml?ziel=Gro%dfbritannien
UK Mobile:
http://wap.teltarif.de/db/res.wml?zi...28Mobilfunk%29
India:
http://wap.teltarif.de/db/res.wml?ziel=Indien
India Mobile:
http://wap.teltarif.de/db/res.wml?zi...28Mobilfunk%29
Bahrain:
http://wap.teltarif.de/db/res.wml?ziel=Bahrain
Bahrain Mobile:
http://wap.teltarif.de/db/res.wml?zi...28Mobilfunk%29
Switzerland:
http://wap.teltarif.de/db/res.wml?ziel=schweiz
Switzerland Mobile:
http://wap.teltarif.de/db/res.wml?zi...28Mobilfunk%29
For his German calls:
Festnet (German landlines) - Local calls:
http://wap.teltarif.de/db/res.wml?ziel=Ortsgespr%e4ch
Festnet (German landlines) - National calls:
http://wap.teltarif.de/db/res.wml?ziel=Fern
All German mobile numbers:
http://wap.teltarif.de/db/res.wml?zi...auer=0&takt=61
If he wants to hear an announcement of the charge per minute before the start of each call, just add the text:
&ansage=1
to the end of each of the examples given above. For example:
UK with tariff announcement:
http://wap.teltarif.de/db/res.wml?zi...nnien&ansage=1
UK Mobile with tariff announcement:
http://wap.teltarif.de/db/res.wml?zi...nk%29&ansage=1
These links can also be used on a mobile phone that has an in-built wap browser.
For the cheapest internet rates (WHICH ARE ONLY VALID DURING THE INDICATED TIME PERIOD!), try:
http://wap.teltarif.de/db/res.wml?ve...=-1&spalten=10
WARNING: Be careful with the "internet call-by-call" link. After the indicated period has ended, you will almost certainly be charged much more per extra minute. Perhaps several cents per minute, or even more than one euro per minute.
A much, much better alternative for cheap call-by-call internet use, is to install the teletarif "Discount Surfer" program, which is available here:
http://www.teltarif.de/click/m:c&a=7...tsurfer/ds.exe
The "Discount Surfer" program is an excellent program. I strongly recommend it. It will enable someone like your dad to always have the cheapest, RELIABLE and LONG TERM call-by-call rate to the internet.
Good Luck!