SIAX does exactly what I would want a native iphone voip app to do (features listed in prev. posts) so, I went ahead and purchased the PRO version.
While the app in its current state is good enough to make great quality sip calls from the iphone over various protocols, I hope the development efforts don't stop any time soon as there are quite a few improvements to be made for the app to be appealing to those potential users willing to pay for it.
Here are some of my comments/recommendations:
1) ver. 1.03 has a new "prefix for contacts" feature and can be found in the Settings menu. In its implemented state, the feature is enabled for all 3 sip accounts I use, regardless whether or not it is needed for that account. It would more make sense (at least for the PRO version) for this to be moved under SIP Account menu so that a prefix can be setup under each of the SIP/IAX accounts one may have, again, assuming multiple accounts.
For me, this would be crucial for any Betamax service which requires a "00" before the country code and number. However, I seem to have found a solution which does not require the use of the "prefix" feature in SIAX (at least not now

). I now have all of my contacts stored in the int'l format,(eg. +15558880101 or +1 (555)888-0101 as displayed in Contacts) and it seems to work in SIAX with any provider requiring to dial a prefix.
2) In the same ver. 1.03, a fix was made so that the app can retain the Recent Calls history (before the fix, Recent Calls were reset upon exiting and relaunching of the app). Now it would be nice to have a way to clear the list.
Also, when I receive a call from another VOIP provider, the SIAX Caller ID displays it as "sip:15558880101@some.ip.address". I tried selecting that from Recent Calls, with no success.
3) The Account Manager displays the sip user name as the SIAX SIP Account name. If one has multiple SIP accounts with the same sip user name, it is difficult to remember which SIP provider each of the SIP accounts belongs to. If the users were enabled to name their SIP accounts at the time of setup, the issue can easily be solved.
4) As a piggyback to item 3 above, the users should also be able to edit sip/iax accounts once they have been setup. In the implemented state, once you set up a sip account, you cannot change anything and are forced to delete and re-setup accounts.
5) Misc. observations: graphics can be at much better quality, especially the bottom menu buttons. On an incoming call, the phone only vibrates and makes a faint beeping sound; there is no way to set a ringtone or adjust the volume. No advanced sip settings are offered (i.e. sip server port, caller id, etc).
As mentioned before, the app is awesome as is because it performs the most important function - VOIP call - extremely well!
Buy one to support the developer!!!
Regards,
AllaNET