What is the difference between the two options for purchasing DIDs?

Individual DIDs no trunk:

Benefit: Less expensive option for users who do not expect their DIDs to require more than 2 incoming calls at a time.

Limitations: You are limited to a total 10,000 inbound minutes regardless of how many DIDs you have purchased. If you have many DIDs then you can reach this limit quickly and may face surcharges of $0.01 per minute for calls beyond 10,000 minutes a month.

DIDs with trunk:

Benefit: Unlimited inbound minutes without any extra cost for going beyond 10,000 minutes. This is the best option for calling card or call center applications that need more than 2 concurrent calls.

Limitations: You are only limited by your trunk size. If you have a 5 channel trunk then you can have 5 concurrent calls at all times. This is a total that is shared across all of your DIDs. If you have DIDs and only 5 channels then only 5 of those DIDs can receive calls at the same time.