Not from the VOIPo line directly. You could use the access number remotely or hit * when your voicemail greeting comes on.
We're working on pushing out some voicemail changes in general soon and when that's done it will support inband. It's just that the current implementation doesn't.
We may be able to add another option like 124 that proxies the call through another system and converts the DTMF so it's compatible with the voicemail system. I'm not 100% sure on it, but can check into it this week.
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