Firstly the good news, OnePlus has started rolling out VoLTE support for OnePlus2 in Oxygen OS 3.5.5. The OTA has reached a very few customers in India till now and that means that it is very less likely that you might have updated your device.
If not then let me tell you this, there are network issues in this OTA which will render your phone useless. You will face signal drops more than twice every minute and you won’t be able to place any calls or use data. If you are using Jio then you are going to face this problem for sure. I updated my phone last night by downloading the ROM from their website and started facing the problems. So please wait till OnePlus releases a fix.
What exactly is the problem?
OnePlus clearly mentioned on their forum that the VoLTE feature might not be working for all the providers and as it turns out Jio is one of them. LTE uses different frequency bands. Based on what speed you require your phone keeps locking itself to the band which suits it the most. Jio is providing its services in two frequency bands : 1800+ Mhz and 850 Mhz but OP2 in the new update keeps trying to switch to different bands and that is breaking something (most probably) because when you lock on to the above mentioned bands using some app like Network Signal Guru then everything works properly.
PLEASE NOTE that I am not an expert in LTE and I am just taking a guess, this might be wrong too.
What to do if you have already updated?
There are a few things which might help you:
- Turn off VoLTE. Tu turn off VoLTE : Settings -> SIM & Network Settings -> VoLTE. This did fix problems for a few people on OnePlus forums but it is very less likely to work.
- Use only one SIM and make sure it’s not JIO. Problem is with the LTE band selection so if you use any LTE network then you will face problems for sure.
- If you are rooted then there is this pretty awesome solution as mentioned in OnePlus forums which helped me ( I have a rooted OP2). Using this solution you can use both SIM data as well as VoLTE.
- Rollback to Oxygen OS 3.10 using the instructions given here: https://forums.oneplus.net/threads/oxygenos-3-5-5-mm-ota-for-oneplus-2.480546/
- Wait for the fix. OnePlus has accepted the problem and are working on releasing a fix very soon.
OnePlus has released a fix for this problem in Oxygen OS 3.5.6. I have tested it and it works without any issues.