Best card for calls from Germany to USA?

[inquisitor]

In Germany neither delivery address nor card holder's address are being checked by payment processors when paying online by credit card, so calling your CC company in order to add some German address is superfluous. What they check is the card's country of origin, so the only problem could be, that certain processors may accept European CCs only.
Remember to order through this link for additional € 5 of credit: http://www.solomo.de/?function=order&affiliateId=3106 (order "Solomo Pro" for cheap international tariffs! "Solomo 08/15" has completely different interational rates!)
Regarding call quality and reliability there's no significant difference to other GSM-operators. However data service is inferior to other German operators, as the E-Plus network does neither support EDGE nor HSDPA, so bandwidth is smaller, and their data service suffers from congestions sometimes. In return E-Plus/solomo is the cheapest provider in Germany.
Btw solomo is a MVNO using the E-Plus network, which is mainly GSM1800 and in places EGSM900 (mostly rural areas) as well as 3G/UMTS2100 (urban areas), so be sure your phone supports at least GSM1800 for comprehensive coverage!
You can check E-Plus' network coverage at http://eis03sn1.eplus-online.de/evportal/portal/gsm