For testing, get a trunk from Callcentric. See this thread for settings:
To test for free: Get an ‘IP Freedom’ plan. You can call their test number 17771234567 (set your Outbound Route to allow this number). To test incoming, call into a SIPBroker gateway; see
and dial *462 followed by your 1777 number.
You can also call out to US toll-free numbers by dialing (for example) **275*18004377950 (set your Outbound Route to allow).
If satisfied, you could sign up for (for example) North America Basic for outgoing and Dollar Unlimited for incoming.
Alternatively, you can do usable testing for free with VoIP.ms or Anveo (in most cases less expensive but IMO support is not as good).