Dual SIM technology has been available for some time now but there is a nifty solution launching very soon to market, called PIECE, that will allow two SIM cards (GSM, EGSM, DCS, or PCS) to be used simultaneously in real time without having to turn your phone off and on to switch numbers.
The PIECE SIM adapter works with any Bluetooth-enabled Android or iOS device (including tablets) and it's the size of a credit card (5mm thick). PIECE features two buttons (function key and main switch), a micro USB port and a micro SIM card slot that enables two active numbers in one phone.

Let's say you carry two phones, a work phone and a private phone. You simply take out the SIM card from the work phone and put it in PIECE.

Then, connect PIECE to your private phone via Bluetooth and so, when someone calls the work phone or your private phone it all happens in one phone. You control your private phone as you would normally, while the work phone is controlled using the PIECE app (on your private phone) to allow you to make calls and send texts.

With PIECE, you can also add calling and text options to Wi-Fi only tablets and add a foreign number when abroad. The built-in 550mAH lithium-ion battery inside PIECE lasts 150 hours on standby and 4 hours talking time.
Other cool features of PIECE include selfie control and the beep alert. When your phone and PIECE are over 15 meters (50 ft) apart PIECE will beep-alert you. You can also use PIECE to look for your phone, or use your phone to look for PIECE.

The Verdict
PIECE dual SIM card adapter fits easily in a front or back pocket, or inside a wallet or purse and essentially allows you to have two numbers on the same phone without having to buy a dual-SIM handset. PIECE dual SIM card adapter accepts any sized SIM card including GSM, EGSM, DCS, or PCS. Once you insert a SIM card in PIECE, it will connect to a smartphone over Bluetooth to allow you to control it from a second phone using an app. PIECE is great for those who don't want the inconvenience of carrying a personal and work phone. The small size of PIECE (83mm tall, 55mm wide and 5mm thick) makes PIECE a very clever tiny companion device to have for adding an extra number to your existing smartphone. Check out PIECE dual SIM adapter