As you have noticed, smartphones with two SIM cards is not NORMAL, there is either a Chinese 'weight' or phone (the same way not really a choice).
I can only assume that the big 'manufacturers' phones are connected to hands and feet with aprosami, through which passes the lion's share of sales of their products, so they're probably not allowed dvuhtumbovye devices (this allows you to circumvent the tariff pits consumers, like incoming on the same tariff, outgoing on the other, and means opsosy losing the loot).
As one example, the fact that opasi was clearly against the introduction of reprogrammable SIM card for a future version of the iPhone, and as I understand apple went on about them.
Now sciphone REALLY stands out among the small selection that is available. Good build quality, no squeaks, no backlash (I personally design 'faceted brick' like more than a 'flat dish'). The problem with the screen is the only visible (unfortunately, this problem POPs up often and many), but not guaranteed, harder is a noticeable lack of hardware accelerated video playback (youtube only plays low quality) and the brake video camera (so that we can assume that the camera is not). But other tasks (Internet, reference books, utilities such as financisto, simple games, etc.) is quite a level.
And most importantly, two SIM cards fully — synchronous online, call hold when receiving a call during a call, the call log shows which SIM was a call (I remember this moment not every phone has), flexible customization of SMS ringtones and phone for each SIM card, works gprs/edge on both SIM cards (unfortunately not at the same time, including when you turn off wifi and gprs, BUT it's linux, busybox ported quite and no one bothers to raise their own connections to configure routing, etc.) there are separate applications for wifi and bluetooth (not tested) tethering...
PS I do not recommend now to take sciphone n21, it is better to wait a bit, I do not cease to hope 2sim devices with android will appear more often, or at least have a sciphone was ideas for a new version with gps, etc.