VoIP - aDSL or sDSL - does it make a difference?

I have some pretty lousy aDSL with a lousy vendor and we're trying to deploy VoIP phones.
We average 50-60 ms latency, but see spikes of 300-600ms.
You can imagine what those spikes do to the conversation on a VoIP phone.
I've tested the latency when there was absolutley no other traffic on the network and found the same spikes.  THis is definitely our ISP causing the spikes.

I've been in contact with another vendor, AT&T.
AT&T offers
3.0Mb/512kb aDSL (cheaper)
384kb sDSL (slightly more expensive)

AT&T boasts a 28ms average, and offers a 40ms guaranteed average, but this is an average.

My question is, will the sDSL provide better latency?  Will sDSL provide better performance and less latency spikes than the aDSL?

My second question is, am I asking for continuing problems?  Should I just bite the bullet and get an internet T-1?

I've read several articles that indicate that sDSL is better for applications such as VoIP, but these articles are pretty dated and reference aDSL speeds that are much lower than todays aDSL up speeds.

Thank you

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you're risking it with any type of dsl technology - it has always suffered from latency problems which voip or video cannot handle very well

your best bet is a dedicated T1 or business cable or fiber to the office from Verizon FIOS. The best value option is business cable and it has gotten very reliable over the past few years.

A client of mine runs 40 phones with maybe about 15-20 simultaneous conversations at any given time. They use packet8 as their voip provider and have had zero issues in the past 3 months. Their download on business cable is 6mbps and upload 1mbps which is more than enough to support all voip phones and internet access at the office

before i forget, QOS is pretty important here at the router and firewall level so that if somebody starts downloading like crazy, your voice packets wouldn't be affected

hope this helps....
A number of factors will cause poor VoIP quality.
A few things you can do-
1. RUN AWAY from your current vendor / ISP if those latency spikes are frequent.
2. use this tool to troubleshoot problems
I LOVE pingplotter it is amazing to see EVERYthing and be able to shove stuff into the lap of the place causing the problem, even if it's your own equipment.
3, Get a device that supports QoS and prioritize VoIP (SIP) Traffic

Now - onto your main question.
SDSL is not imperitive, especially with aDSL offering speeds that smack it back to the dust, usually the only things you get with sdsl are QoS and commited data rate guarantees. after working in support for an number of ISP's i have found that it is really hard to hold them to those agreements.

Just get the fastest ADSL you can find for your money
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