If your just starting out i would recommend using these guys:
Been with them for 2 years only ever had one down time with them, and their support is great. Don’t worry not trying to sell you anything, thats why i am giving you a direct link to them.
I have used them for DB intensive stuff and never had a problem, everything always worked fine, if what your doing become intense for the server they have you on, they just auto move you onto a more powerful one, however though they will only do that maybe one or two times, after that they may offer you a Dedicated server at a discounted price, which by the way are damn cheap.
The bandwidth allocation is pretty damn good as well, for me personally and my toy websites i use the $2.99 a month one, i just pay a year in advance cause you then get double up on Bandwidth and disk space, i host all my projects on there before going live with anything, if it don’t fail on there, it wont fail when it goes live as we use pretty powerful systems in house. They also use Cpanel which for me is the best in my books, i don’t think there is anything out there that can match Cpanel.
If your doing Calling Card and using Asterisk, i dare say your using MySQL as well, and if that is the case, you can have more then 1 DB as you can see on their site it goes up to 20 DB’s on their top shared hosting plan.
Anyways just a thought, best off to save as much money as you can when first starting out, but you also have to try and not loose quality of service as well, so what ever you do make sure you don’t make a quick decision.