帐户停止活动
如果您有Google语音号码，但在9个月内既没有拨出电话或收到来电，也没有发送或收到短信，则Google会收回该号码。不过，Google不会收回已转携至Google语音服务或申请了永久使用权的号码。
个人猜测，这里的申请永久使用权的号码，应该就是$20买断的那个号码。
原因分析：
一个账户只允许一个google voice号码，如果需要绑定第二个，那么必须给google缴纳20$
那么长久保号的方案就来了：【共计花费30美金】
1 先搜索一个新的号码，并且花10$注册
2 90天内，你的旧号码会显示过期，点击购买，花费20$ 买断。【你的过期日会消失】
官网链接
https://support.google.com/voice/answer/115114?hl=en
Keep your original Google Voice number
You'll be charged a $20 fee to keep your original Google Voice number as a secondary number. If you had previously ported in that now-secondary number, you won't be charged.
Calls and text messages to both numbers will reach you. But outbound calls and texts will only be sent from your primary Google Voice number. You can swap them at any time.
【这一条比较重要，给大家翻一下，意思就是两个号码都可以收短信和听电话，但是只有主号码才可以呼出和发送短信】
Within 90 days of porting a number, open Google Voice on your computer.
At the top left, click Menu Menu and then Legacy Google Voice. Google Voice will look different, but you're in the right place.
At the top right, click Settings Settings and then Settings.
Click the "Phones" tab.
Next to your old number, click Make permanent. To confirm and pay, follow the onscreen instructions.
After you pay, the expiration date next to your original Google Voice number disappears.