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I have a Nexus 4 with Kitkat, working fine with t-mobile (USA). Yesterday, I did an OTA to Lollipop (LRX21T; baseband M9615A-CEFWMAZM-2.01701.04). But after that the cellular network only briefly works.

First problem, I encountered was the lack of data connection, but after I changed the APN setting, it worked...but only briefly. Every time I reboot the phone, it can make phone calls, and access the data network for a few minutes (or sometimes I have no access to begin with). But then the network indicator becomes either an 'empty triangle' or a 'full triangle with an exclamation point'. Then, I can't make phone calls or use the data afterwards.

Very strangely, I just found out that if I connect to wifi, I can make phone calls suddenly. If I turn off wifi, I can't make phone calls any more. What is going on?

Does anybody have the same problem? Does anybody a known workaround?

My current APN setting is:

T-Mobile GPRS

APN: fast.t-mobile.come
Proxy: not set
Port: not set
Username: not set
Password: not set
Server: not set
MMSC: http://mms.msg.eng.t-mobile.com/mms
MMS proxy: not set
MMS port: not set
MMC: 310
MNC: 260
Authentication type: not set
APN type: default,supl,mms,dun
APN protocol: IPv4
APN roaming protocol: IPv4
Bearer: unspecified
MVNO type: none
MVNO value: not set

Further testing using *#*#4636#*#*

  • GSM service: in service
  • GPRS service: disconnected
  • Network type: UMTS
  • Call redirect: false
  • Call status: idle
  • radio resets: 0
  • data attempts : 0
  • data successes: 0

  • cellinfolistrate 2147483647

  • IMS registration required is 'off'
  • SMS over IMS is 'off'
  • SMSC: _______ [update][refresh]
  • Toggle DNS check: 0.0.0.0 not allowed

EDIT: During the moments when the network works, GPRS service is 'connected'.

EDIT2: If I force using 2G, it works fine. Just with unbearably slow speed.

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UPDATE2: After a while, it seems like it cured itself. No more connectivity issues for a full 24 hrs. Perhaps it was a bad tower-radio(baseband) combination?

UPDATE: Actually, this didn't fix it completely. It behaves better, but it eventually goes into a state where the antenna says 3G, but there's no data nor phone connectivity. This happened 3 times.

So, I think I fixed it by updating the APN address to epc.tmobile.com, switching to 2G only and rebooting, switching to 3G and rebooting.

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