Nokia vs Android, why such a strong difference in the quality of sip telephony?

Question

Android

Good afternoon.
There is a Nokia E66 with a native SIP client and Jiayu g3s on which many sip clients have been tried (provider Zadarma). In the first case, the connection quality is very good even on an EDGE connection, in the second case it is impossible to talk even on wi-fi. Tried the native Zadarma client, csipsimple (I've settled on it for now) and a few others that are recommended on the Zadarma wiki with recommended features, but have not yet found a satisfactory option.
I understand that the matter is in the settings, but what and where? Maybe that android cuts the channel or something else?
Thanks in advance for your help!

Answer 1

Provider name problem

Answer 2

Nokia probably uses g729, install it in your android clients (you need to buy it in csipsimple)

Answer 3

CSipSimple has SILK audio codec, try it.

Answer 4

The csipsimple itself may not include G729 on all phones (licensing issues, the codec seems to be available for private use in the CIS).
Try:
1. remove all codecs except the test codec
2. if it doesn't suit you or doesn't work 729 try speex or gsm, both are supported in Zadarma