CSIPSimple is #5 in Top 11 SIP Softphones
Native sip app for android device. SIP for calls and instant messages. Android integration with rewriting and filtering rules. Echo cancellation (with various backends : webRTC, speex, simple).
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#5 in Top 11 SIP Softphones
The best alternatives to CSIPSimple are: Linphone, Bria, Zoiper, 3CX Phone, Truphone