1. ftap's Avatar
    Just wanted to let everyone know that the hardware at this time does not support LTE data while on a voice call.

    Usually this isn't an issue. But if you tether and are on a 60 minute conference call and expect LTE data off your tether plan. You are in for a rude awakening.

    Try it out for yourself. AT&T tech support confirmed this to me.
    04-20-2012 07:35 PM
  2. mayoo's Avatar
    Same with Rogers. I thought that's by design ?
    04-20-2012 07:38 PM
  3. ftap's Avatar
    From what I've read it has to do with circuit-switch fallback (CSFB) technology.

    Something that has to deal with falling back to 3G during voice calls. And the tech is just not there for true voice of LTE calls yet. Heard its being. Tested out and may not be read well into 2013.
    04-20-2012 07:55 PM
  4. alpinestars1z's Avatar
    From what I've read it has to do with circuit-switch fallback (CSFB) technology.

    Something that has to deal with falling back to 3G during voice calls. And the tech is just not there for true voice of LTE calls yet. Heard its being. Tested out and may not be read well into 2013.
    Isn't it same for Verizon too? No voice over LTE yet? Isn't it still being tested?

    Either way, it's still going to take a while. According to this, Qualcomm and Ericsson successfully completed the first voice call handover from an LTE mobile network to a WCDMA network only a couple months back.

    Qualcomm voice over LTE test hints at a complete 4G future - Pocket-lint
    04-20-2012 08:02 PM
  5. KDarling#WP's Avatar
    Isn't it same for Verizon too? No voice over LTE yet? Isn't it still being tested?
    Right, nobody has VoLTE yet.

    However, Verizon's LTE phones have two separate radios, so they simply turn on the CDMA radio for voice calls... without having to drop LTE for data, as AT&T single radio phones must.
    04-21-2012 10:55 AM
  6. callagent007's Avatar
    Just wanted to let everyone know that the hardware at this time does not support LTE data while on a voice call.

    Usually this isn't an issue. But if you tether and are on a 60 minute conference call and expect LTE data off your tether plan. You are in for a rude awakening.

    Try it out for yourself. AT&T tech support confirmed this to me.
    This is because of Circuit Switch Fall-Back (CSFB) being used today for enabling a "traditional" Switched Circuit-based telephone call when under 3G/UMTS and LTE coverage.
    For more details check out: 3G and 4G Wireless Blog: Circuit Switched Fallback (CSFB): A Quick Primer

    I would be curious to know what is the end-to-end setup delay affecting a voice call between two users under LTE coverage, i.e. causing CSFB on both legs of the call...
    Is that something acceptable or definitely not?

    TIA
    07-07-2012 10:20 AM
  7. jdevenberg's Avatar
    It isnt so much that they disable it as it is a technology barrier. If you have two radios (like Verizon has to do) you can do 3G voice and lte data, but having two radios very negatively impacts battery life. If you have one radio, as AT&T does, it can only connect to one network at once. So if you are making a call, your phone goes to 3G, since no network supports voice over lte yet. Since you have to be on 3G for your call, you have to use 3G for data as well.
    07-07-2012 11:39 AM
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