My ISP currently has a severe outage, which is why I'm tethering my Android phone and a MacBook over WiFi. The Android phone is a HTC Desire GSM running Cyanogen 7. I have a stable HSDPA/EDGE connection.

Now, as this is my only phone, it rings from time to time. But whenever it does and I accept a call, the mobile data connection is lost or cancelled. Same for placing calls. Writing texts won't cancel the mobile data connection.

So, whenever I am on the phone, the internet connection goes dead.

Why is this? Is there any technical limitation that won't allow one to call and send/receive mobile data at the same time? If not, can you somehow trick Android into not cutting the connection?

  • What network are you on? Jul 20, 2011 at 14:36
  • My carrier is "bob", which is a subdivision of A1 Telekom (warning, German page). They offer a basic GSM network with UMTS/HSDPA data, my phone occasionally switches to EDGE when reception gets worse.
    – slhck
    Jul 20, 2011 at 14:40
  • Hmm, I can't find any info on whether they support DTM. Jul 20, 2011 at 14:45

2 Answers 2


Most HSDPA / EDGE CDMA networks don't support data and voice at the same time. CDMA Modern GSM networks (including 3G and HSDPA, but not EDGE) do, and LTE will, so I'm not sure why you're having this problem.

It's possible that Dual-Transfer Mode may not be enabled on your phone. Alternatively, your network might not support it. (Info on DTM.)

  • Okay, seems that's just how it is -- still: Do you happen to have a source? You know, [citation needed], I'd love to read about that!
    – slhck
    Jul 20, 2011 at 14:02
  • This is backwards, isn't it? Jul 20, 2011 at 14:13
  • @eldarerathis This is what I get for answering questions on my phone after I wake up :P I don't read things properly. Yeah, CDMA's generally the one that doesn't support simultaneous voice/data. Unfortunately I can't find any particularly reliable resources. Jul 20, 2011 at 14:24
  • @slhck So I think this is wrong ... you should probably un-accept. Jul 20, 2011 at 14:24
  • 1
    @Matthew: I can't find anything "official" about CDMA not supporting it, but here's AT&T stating UMTS/HSDPA supports simultaneous voice and data: developer.att.com/developer/forward.jsp?passedItemId=2400252 Jul 20, 2011 at 14:31

It all depends on who your mobile carrier is. I have AT&T and they allow one to surf and talk at the same time. This is because their networks are CDMA.

If you want to surf the web while you're talking on the phone it sounds like your only option right now is to change carriers.

  • Since Europe's never going to see CDMA, I guess there's no option to switch. There are US carriers that use GSM?
    – slhck
    Jul 20, 2011 at 14:03
  • 1
    Source? AT&T has always been GSM as far as I'm aware. Jul 20, 2011 at 14:21
  • 2
    Close. AT&T is W-CDMA which is based on UMTS, a GSM technology. Source. I think the distinction is between technology sets and protocols ... CDMA protocols can be used on a non-CDMA network, if I'm understanding this correctly (no guarantees). Jul 20, 2011 at 14:25
  • 1
    @Matthew Read this, it should be under network design. Is this what you're looking for? Jul 20, 2011 at 14:43
  • 2
    @Matthew: That's correct. CDMA is just a protocol ("channel access method"), but it's used colloquially to refer to the implementation in the case of carriers like Sprint and Verizon, which is kind of confusing... Jul 20, 2011 at 14:44

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