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Something we’ve noticed when shopping for dual-SIM phones is that the manufacturer very rarely provides any information about the functionality other than it exists. It doesn’t tell you how dual-SIM works in practice, nor whether both SIMs support 3G, or even what size SIM cards they accept. As we’ve learned, you can never assume: you’ll need to contact the manufacturer or check spec tables, reviews or forums to find out this information.

For that latter concern, as technology journalists who are always having to swap SIMs between the various phones we have in for review, we have found the best solution is to adopt a nano-SIM for our

personal smartphone, then pair it with an adaptor when we need to use it in a phone that supports full-size- or micro-SIMs. SIM adaptors are very cheap, but some are better than others. We like the MediaDevil Simdevil, which comes with nano to micro, nano-to mini and micro to Mini adaptors, plus a SIM tray ejector tool. It costs £3.97 from amazon, If you’re planning to stick with the phone,

however, you can always request a new SIM of the correct size for free from your network operator, then swap over your number.

In all the dual-SIM phones we’ve tested both SIMs are on standby at all times (known as dual-standby phones), but you can actively use only one SIM at a time. This means that either SIM can accept a phone call or text at any time, without you having to actively swap between them or reboot the phone. However, if you get a call on one number while a call is active on the other, it won’t start ringing in your ear or give you the option to put the first caller on hold  the call will simply not be successful.

Dual-active SIM phones also exist, however, which use two modems and allow you to receive calls on both numbers at once. We’ve not tested any dual-active phones, but some more recent examples allegedly include the dual-SIM variants of the HTC One M8, Sony Xperia Z3 and Samsung Galaxy S5 mini. (Always check before you buy, of course.)

If it’s you who wants to make a call or send a text, Android has a standard SIM Management menu that lets you specify which SIM should be used for voice calls, video calls, messages and mobile data. You can either specify a particular SIM for each of these tasks, or leave the setting at Always ask. If you choose the latter, the next time you want to make a call or send a text, you will be asked which SIM you want to use. Motorola improves on this with its dual- SIM Moto G, with its Automatic SIM selection able to track your SIM usage and then suggest or automatically use a particular SIM for a certain mode of contact. The data connection is where there seems to be a lot of confusion when it comes to dual-SIM phones. Whereas both SIM slots on some dual-SIM phones are capable of supporting 3G connections (for example, the Elephone P5000 reviewed on page), you can use 3G on only one SIM at a time.

Calls and texts the data connection can’t be on standby for both SIMs: you must specify which SIM you want to use rather than select one when prompted. Of course, this isn’t always the case, and

the ZTE Blade S6 (read our review on page  supports 3G/4G only on its first SIM slot, and you can’t change the data connection for browsing the web or making video calls. You can still specify which SIM should be used for calls and texts, although things look a bit different in Lollipop. By default, when you are using the data connection on one SIM and a phone call comes in to the other it will pause the data connection on the first. In the Moto G, you’ll find a Connection priority menu, which allows you to specify that calls should instead go to voicemail instead of interrupting your browsing. There is no such option on the other dual-SIM phones we’ve tested, but it’s not something we’d be likely to change in any case.

The Elephone P5000 momentarily threw us when we attempted to switch the data connection from one SIM to the other. When we tried to change the data connection from O2 to Vodafone, it displayed a message suggesting that 3G wasn’t supported by the Vodafone SIM. We knew it was, which suggested that the second SIM slot it resided in was capable of 2G only. In fact, we found

that if we first changed the Video call setting from O2 to Vodafone we could then change the data connection without issue. (Note that if your data connection is ‘Off’ this is because your Wi-Fi is switched on.) Which SIM is configured to use the data connection is instantly evident from the navigation bar, with the SIM in slot 1 displayed in blue and the SIM in slot 2 displayed in green. One will be marked with G and the other 3G.

You can change these colours and whether or not the phone number is displayed within the SIM Management menu to make it more instantly obvious which is which. Both the Moto G and ZTE

Blade S6 also allow you to change the SIM card name. Another issue when using dual-SIM phones is where your contacts are stored. We found that by default the contacts from both SIM cards are stored in the phone book. If you’d rather see the contacts from only one SIM, tap the three dots icon at the bottom right of the screen (within the Contacts app) and choose ‘Contacts to display’. You can then select All contacts, Gmail contacts, phone contacts or one of your two SIMs. Usually when you add a contact you get a pop-up menu asking whether you want to store the contact on your phone memory,

your SIM or your Google account. Here you’ll now see two SIMs in the list rather than one. A quick way to turn this off and prevent you always having to choose is to open the SIM management menu, select Contact binding and then select a specific SIM.

Most of us have experienced the sickening feeling that strikes when you accidentally delete something important. Adding a Recycle Bin to your Android device provides a safety net in case you erase some valuable photos or videos. Dumpster (play.google.com/Dumpster) is an excellent free bin for Android phones and tablets - and you don't have to root your device to use it.

it lets you ‘undelete' almost every file type and will soon have the ability to restore deleted text messages, contacts and apps. On iPhone and iPads, you can recover accidentally deleted content using an app such as Leawo iOS Data Recovery (www.leawo.com). It's not free in fact it's pretty expensive at $69.95 (£41) but there is a trial available.