One problem that I see (you guys might already address this) but if I'm a helper and I get a call from a blind person and I have just a couple minutes to help but the blind person needs 10 minutes of help it would be inefficient to connect me with them. One way to solve this would be for the blind to select a time range of how much help they need (1 minute, 5 minutes, 10 minutes, etc...) and then when it calls the helper it will show how much help is needed, so they can either decline or go into the call knowing how long they will be busy for.

Also you may be able to introduce pricing in this way, where anything under 5 minutes is free, but over 5 minutes you charge however much per minute and then split the cost with the helper.