Does trimmed SIM card affect iPhone 4S's signal strength? I have just received my iPhone 4S ordered online. I don't have a microsim card that iPhone 4S would need to me to. I don't wish to pay extra to buy a micro sim card since it doesn't give much improvement. I did a search and found out that I could cut my ordinary 3G sim card to the size of a micro sim card. And I did this.

So now, I put that trimmed micro sim card into my iPhone 4S and it worked. But, the reception meter has only 2 bars all the time! The phone may be able to access the web and send sms through the cellular network but having only 2 out of 5 bars at the reception meter makes me feel totally unsafe; I am doing all of these at my home, where the reception signals are usually very strong.

When I put the same trimmed sim card into another iPhone 3GS, the reception also has only 2 bars. But when I put the trimmed sim card into an iPhone 2G, it has 5 bars.

What's wrong? Is it my iPhone 4S or the sim card that is having the problem? What problem am I having and what else can I do?

Update

So the 5 signal bars on iPhone 2G is merely the 2G network. When the 2-bars 3G signal on my iPhone 4S drops to only the 2G network, it also has 4-5 bars of signal strength but that's 2G. Does trimmed SIM card has problems with 3G networks?
No - the sim card only provides an ICCID number to the phone. That number is read once per boot as the phone just uses the sim to identify what account to bill for service when registering with the nearby cell towers (IMEI and ICCID together let the system know what number to assign your phone and who to bill). 

Something else must be causing your observed behavior. 

Keep in mind, there is no guarantee two phones in the same location are not on distinct cell towers. Especially if one tower is overloaded or doesn't have high speed data so the phone /carrier might pick a faster connection that happens to have less bars of signal. 

What does your carrier say if you call them for a site survey / diagnostic?