Making Use of a Separate Phone & Data SIM in a Smartphone

The situation couldn't be more difficult for users with two SIM cards. Some cellular phone providers (network operators or carriers) offer cheap rates on voice calls others are cheap on data plans. Typical scenarios include a  business SIM card and a private one as well as one for long distance/intercontinental calls and the other for national calls, etc. There are many scenarios on this but all have one thing in common:

I for one, have a business Vodafone SIM card and a cheap SIMYO 1 GB data option for as low as 10 EUR/month.
At present, 1GB for mobile phone users seems to be a flat rate and even when connected to a notebook or netbook this seems to be more than sufficient. Latest carrier statistics say, that even heavy iPhone usage produces approx. 450 MB by average, but this is predicted to change significantly until 2013, as Cisco has recently pointed out in one of their research papers.

The ideal solution for me is to run most of the times on the SIMYO SIM card and switch to the business phone for outgoing business calls. One might ask about incomming business calls via Vodafone while registered with SIMYO. The solution is as clever as easy. I have configured a call diversion on the Vodafone SIM as long as I am not registered with the network. This means the phone switched off or is out of range of the Vodafone network. Thus, I am reachable directly under Vodafone once I registered with the network and reachable via a call diversion once I am registered with the SIMYO network. Costs for a call diversion are considerably lower by using the 1 GB data tariff with SIMYO. Thus, it's plausible to give a piece of plastic a try and save a lot of money surfing the net all inclusive for a fixed price.

A so-called twin SIM adaptor is the solution, which means nothing more than to place the two desired SIM cards into a holder which lead into another SIM card shape for the smartphone's SIM interface. A typical twin SIM card adaptor has some flat cables connecting the single SIM to the other two SIMs. A logic on the adaptor then switches between the SIM cards. Because of the digital cellular network's architecture (GSM or UMTS) it is not possible to be registered with both identities at the same time (this would require two transmitters, which go into too much detail to explain).

There are analogue and digital twin SIM adaptors. The main difference is, that the new digital ones integrate seamlessly into the smartphone's menu structure (e.g. Symbian, Windows Mobile, etc.) and thus allow for hot switching to the other provider's network. The old analogue one does not feature a menu entry and always require switching the smartphone off and on again in order to switch the network. The advantage of the analogue adaptors is that they definitely will work properly with any mobile phone regardless of how old it is, which operating system it runs and whether or not it is 2G or 3G (GSM, EDGE or UMTS).

The device of choice for this experiment is a Treo 680. Accordingly, I decided to go for the analogue rather than for a digital one, mainly because I did some research in advance and heard that this adaptor in particular would function without any problems.

Once decided that I would go for an analogue twin SIM adaptor, I ordered online. After a couple of days I received a regular envelope with the SIM adaptor inside. One should note that the SIM adaptors are more or less universal and not for a particular phone. In addition, the smartphone never had been designed to give enough room to place another piece of plastic somewhere, so one should make sure in advance that 3 millimeters can be spared out somehow. Thus, a twin SIM adaptor might not fit perfectly but will work.

Installation of the two SIM cards is easy and mostly done without reading the installation instructions, as shown in the image above. Installation of the adaptor is a bit tricky - because of the fact that the Treo's battery fits pretty well. There is not enough space between battery and cap to close it as easily as without the adaptor. Patience is a good trait here and some practical skills during installation are recommended as well.
I decided to place the twin SIM adaptor below the battery and the thus. The flat band cable is slightly bended as a result, but that seems not to be a problem. The biggest challenge is the reinstallation of the Treo's back, because now it will fit very snugly.

As one can see in the picture, the battery keeps staying at an angle and does not fall into its desired place again on its own. Thus, firm pressure is needed in order to reattach the Treo's back plate and to not destroy any of the plasitc parts.

I am happy with the result. Once the back plate is closed again, the Treo looks normal with one exception: I recognized a slight gap of 1 mm between the SD card cap and the right side mechanics. This points to some internal pressure between battery and bottom, of course, due to the twin SIM adaptor.
Apart from that the Treo is still the same :)

After inserting the battery and reattaching the Treo's back, the device powered up and registered with SIMYO properly. Thus the physical connection of the card adaptor was good. Switching the network required me to power off and on again. I pressed the red phone button for two seconds to disconnect, and then again in order to switch to Vodafone. After 1 minute I was booked into the Vodafone network and happy about the ease of having the freedom of choice between two networks I need to use and I would like to use.

It also should be noted, that I could reproduce network registration times with SIMYO of about 30 seconds whereas it took 60 seconds to register with the Vodafone network.

Now, I am surfing the net with SIMYO and receive calls on my SIMYO SIM card as well as calls from my Vodafone card, which are forwarded to the SIMYO card. Thus, I am reachable under two different numbers at the same time. This is great because I don't have to tell my business partners the private cell phone number and confuse them of how to reach me. In case I need to call somebody via my business number, I switch off and on again, and after 1 minute I am ready to go...

The adaptor retails about 20 EUR and can be ordered online at 2-phone-in-one.com. They even feature triple SIM adaptors, but that's a different story... :)

In a following blog entry I will detail on how to automatically switch between networks by certain events and why this should be useful.