Please clarify if by lines you mean separate VoIP accounts or number of 'line appearances'
Each VoIP account can carry multiple virtual 'lines' (also known as channels), however your provider may restrict the number of concurrent channels that you can use.
It is common for VoIP providers to limit you to 2 concurrent channels so that you can have Call Waiting. Most providers will charge for each additional channel (last time I checked it was about $30 USD per channel per month (unlimited calls on each channel) on average - this may have changed however.
Some providers will provide unlimited channels if you agree to pay per minute of use.
If Express Talk is limiting you so that you can only register two VoIP accounts, you should contact NCH support... however having said that, it would be very unusual for you to need so many different registered VoIP accounts. As I said earlier, each account/line can carry multiple channels (or virtual lines), the only reason why you would need to register multiple VoIP accounts is if you are signed up with many different VoIP phone service providers.
Please explain your situation further and I will try to help you solve your problem without needing so many VoIP accounts (perhaps the use of a PBX would help?) - as I indicated earlier, it is very unusual to need so many.