Hello.
I have been using
http://www.bestvoipreselling.com as a trunk with a2billing for quite long. I can say it is has been reliable for my service. bestvoipreselling offers a reseller interface so you can become a voip reseller. they also allow you to set your own calling plans and they provide mobile phones and pc soft-phone along with a calling cards platform.
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WHMCS is an all-in-one client management, billing & support solution for online businesses. Handling everything from signup to termination, WHMCS is a powerful business automation tool that puts you firmly in control"; this is how whmcs define themselves on
http://WHMCS.comITSP from http://www.telemoip.com is a Powerful Whmcs Module designed to integrate VOIP API into Whmcs allowing every one with Whmcs installation to add VOIP packages and build a 100% white label VOIP telephony provider.
using ITSP to connect whmcs to bestvoipreselling API was such a clever idea. Now I have a very powerful control on my business, in fact all my business process are automated thanks to whmcs, and I can concentrate much on getting more customers now.
one disadvantage of this solution is limitation to only bestvoipreselling as trunk, but I am happy with this for now, since I get very good rates and excellent call quality and using ITSP provide me with more power upon my customers.
From my perspective this solution is a very good start for any one who wants to start with voip business.
I hope this was useful for every one.
I am not associated or affiliated with any of the companies above; I am just a very happy customer!