You can also send and recieve SMS on the PORTech Gateways via AT commands over a socket connection, I've not checked but would assume all other AT commands will work so you can check signal strength etc this way also.

Steve

Message: 4
Date: Wed, 17 Jun 2009 23:31:06 +0200
From: Jan Kubr <jan.kubr@gmail.com>
Subject: Re: [Freeswitch-users] Which GSM gateway to buy?
To: freeswitch-users@lists.freeswitch.org
Message-ID:
<698401620906171431t10432015xa78976a401dc5c5b@mail.gmail.com

>
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We plan to buy one of these:
http://www.2n.cz/products/gsm_gateways/voip_gsm_gateway/voiceblue_enterprise_voip_gsm_gateway.html
since you can use SMTP/POP3 to manage SMS.

Jan