The easiest way is to insert a sim card from any network (let's say Orange) and then do a network scan. Most devices will display the results in order of signal strength with the "home" network at the top. Let's assume the results list looks like this:
Orange
Voda
Three
o2
T-Mob
Next, try a different sim card and do the same thing. Let's assume that the result on a T-Mob card is:
T-Mobile
Orange
Voda
Three
o2
Putting the two lists together enables you to conclude that the best network will probably Orange because it comes higher than Voda on the second test and we already know that T-Mob has the poorest signal.
If you have an unlocked iPhone with a couple of spare sim cards you can do a field test for network strength as follows:
– Type *3001#12345#* followed by a tap of the Call button.
– This brings up Field Test mode.
– The signal strength bars in the upper left are replaced by a negative number.
– The less negative the number, the better your signal strength. For a reasonably reliable signal, the number should be less negative than -100. Ideal strength would be somewhere around -50.
If you've not seen them, Ofcom recently produced 3G coverage maps which showed the order of best 3G network coverage as follows:
1. Three
2. Orange
3. T-Mob
4. Vodafone
5. o2
Three have a roaming deal with Orange and tend to be cheaper, so for the best coverage Three offers the biggest standalone 3g network which they are still merging with T-Mob's – then a free roaming agreement onto Orange for the places that Three and T-Mob don't cover – which tend to be few and far between.
