It’s almost been a month of using the iPhone and thus AT&T. AT&T (along with T-Mobile) is a GSM network while Sprint (along with Verizon) is a CDMA network. For the end user the difference isn’t very noticeable in most cases although if you’re in the Midwest you’ll likely noticed better coverage with CDMA.

GSM has two major advantages over CDMA for the end user. The first advantage is the fact CDMA phones use a SIM card which can be taken out of one phone and inserted into another (so long as the other phone will work on the first phone’s network). If you want to swap CDMA phones the process is generally more difficult (for example on Sprint you need to log into your Sprint account online and enter in a series of numbers on the new phone). The second advantage is the fact on a GSM phone you can use both the voice capabilities and data at the same time. With a CDMA phone if you’re talking to somebody you can’t use data and if you want to use data you can’t call somebody. Even though there is no reason for this Sprint has even locked the Evo 4G into not allowing voice usage and 4G data usage at the same time (with 3G it’s a limitation of the hardware/protocol while with 4G the restriction is purely artificial).

Well it dawned on me when somebody called me and asked a question that required I look something up. I told them, “Hold on a second I’ll look it up and call you ba… wait hold just a second” and discovered the wonders of a phone that can use voice and data at the same time. Huge advantage.

I also learned that there apparently isn’t any additional cost to use call forwarding on AT&T, just just consumes your minutes. That means when I travel back home (where I have no AT&T coverage but have Sprint coverage) I can set my iPhone to forward calls to my Evo without having to rack up Sprint’s 20 cents a minute for forwarding calls charge.

There certainly are downsides to AT&T (their data plan is fucking horrible compared to Sprint’s) but there are also some upsides.

3 thoughts on “GSM vs. CDMA”

  1. The other big advantage of GSM is if you travel overseas. I can use my normal phone when I am in Europe or Mexico with no issues. Can also drop in a local SIM there and have a local number.

  2. GSM…

    1) Often you can’t use the same phones in Europe because of different frequency bands.

    2) iPhone uses non-standard SIM cards

    3) Verizon = coverage, AT&T = poor coverage and lots of dropped calls.

    1. 1) Usually you can use the phone in Europe but your data plan may or may not work (not always the case of course). It’s akin to using an AT&T phone on T-Mobile or visa versa.

      2) The micro-SIM used by the iPhone is a standard that was developed by the European Telecommunications Standards Institute. You can put a micro-SIM into a phone that uses a standard SIM by using a plastic adapter (although not visa versa). Micro-SIM usage just isn’t as widespread yet as the standard SIM form factor.

      3) No arguments on coverage. I have zero coverage back in my hometown on AT&T while Sprint has coverage there. I haven’t experienced any dropped calls with AT&T though.

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