1. There are a couple of things you can try but this could be a problem with poor coverage. In the softphone, tap on settings, then SIP Accounts, then your SIP account. Tap on advanced settings, then codecs for wifi. Move G.711 ulaw and G.711 alaw to the disabled section. Be sure to save the change. This will ensure that only the low bit rate codecs are used when you're using 3G. If you haven't already, you may also want to purchase the G.729 Annex A codec. This is a high quality, low bit rate codec that is usually good for 3G/edge calls. Unfortunately, I can't guarantee this will improve the quality since it is possible the issue is something we have no control over. Even though more and more carriers are allowing VoIP over 3G, some of them just don't have the coverage to provide good quality calls over 3G. Also, I've heard that some carriers, while they don't actually block VoIP or SIP, do something to RTP traffic that greatly reduces the audio quality. One other thing that you might try is adjusting the packet size. Go back to codecs for 3G and you'll see the setting for packet size. Increasing the packet size uses less bandwidth since less total packets will be sent, but lost packets might be more noticeable since more audio is contained in each packet. We've tried to make the codecs as customizable so customers can experiment to see what gives them the best results.
2. If you're having an issue with DTMF tone, I would recommending turning 'Send all Enabled' off and moving audio to the disabled section. If you still have an issue, try enabling only one Mode at a time. Try rfc 2833 first, if it doesn't work, try enabling just SIP INFO. I'm pretty sure one of them will work. We've made the DTMF Mode extremely customizable as well.