As I mentioned here in Europe it is a ***** with different ( local) operators when traveling. so Dual SIM cards adapters is not that unusual. and one of the most respected companies is this http://www.simore.ch/en/index.php I have never used their products so I cannot say too much.

nowadays ( here in EU) it is not Phone Calls that is making a hassle, as call rates are acceptable even by using your local ( another country SIM) but instead it is Mobile Broadband that is difficult. ( as I use Skype, email , surf. GPS Maps)
and THAT be really expensive like € 15 / Mb, ( $20.-)
this have been my biggest issue when on travel