Hey,
In some DCs I've done mutual OOB swaps with other telcos in the same suite, this is usually cheap or free (excluding the one time xconnect
We consciously decided to not ask or accept OOB swaps, because of fear that they might be provisioned outside processes which might make it impossible to repair them through normal commercial processes, which would potentially cost lot of downtime and NOC's resources.
Sometimes the DC provider has an OOB connectivity service that uses separate transit providers than we use and this often cheap too. Again this is often bespoke per DC/colo provider though.
MRC quotes I have 400USD Equinix, 288USD Terramark, 300USD Coresite. Compared to PSTN which we see at 90-150USD. This makes me less inclined to focus on HW CAPEX and optimise for HW/SW that tooling and people already support.
The most scalable solution I've been involved in so far is VDSL. Here in the UK lots of DCs are on-net for the national incumbent VDSL
I think WAN indeed is very market situational, and if you need to support world, it is beneficial to have solution which supports many WAN options, without needing external boxes and external power bricks. We try to do just ethernet, but even that is already being provided as copper, fibre and in one market with PPPoE, all which are non-issues by going with Cisco. I do wish I had second option, I do wish JNPR SRX would support async serial ports. -- ++ytti